518 
M4 


GIFT  ©F 
A.    P.    Morrison 


THE 


ABC 


OF 


ELECTRICITY 


BY 


WM.   H.   MEADOWCROFT 


NEW  YORK 

AMERICAN    TECHNICAL    BOOK    COMPANY, 
45  VESEY  STREET. 


SIFT  OF 


COPYRIGHTED,  1888, 

BY 
WM.  H.  MEADOWCROFT 


Q(L 


FROM  THE  LABORATORY  OF  THOS.  A.  EDISON. 
ORANGE,  N.  J.,  Sipt.  4,  1888. 

MR.  W.  H.  MEADOWCEOFT, 
New  York  City. 

DEAR  SIR  :— 

I  have  read  the  MS.  of  your  "  A  B  0  of  Elec- 
tricity," and  find  that  the  statements  you  have  made 
therein  are  correct.  Your  treatment  of  the  subject, 
and  arrangement  of  the  matter,  have  impressed  me 
favorably. 

Yours  truly, 

THOS.  A.  EDISON. 


M99151 


PREFACE. 


WHILE  there  is  no  lack  of  most  excellent  text- 
books for  the  study  of  those  branches  of  Electricity 
which  are  above  the  elementary  stage,  there  is  a 
decided  need  of  text-books  which  shall  explain,  in 
simple  language,  to  young  people  of,  say,  fourteen 
years  and  upwards,  a  general  outline  of  the  science, 
as  well  as  the  ground-work  of  those  electrical  inven- 
tions which  are  to-day  of  such  vast  commercial  im- 
portance. ^ 

There  is  also  a  need  for  such  a  book  among  a 
large  part  of  the  adult  population,  for  the  reason 
that  there  have  been  great  and  radical  changes  in 
this  science  since  the  time  they  completed  their 
studies,  and  they  have  not  the  time  to  follow  up  the 
subject  in  the  advanced  books. 

As  instances  of  those  changes  just  spoken  of,  the 
electric  light,  telephone  and  storage  batteries  may  be 

mentioned,  which  have  been  developed  during  the 

5 


6  PREFACE. 

last  ten  or  twelve  years,  with  the  result  of  adding 
very  many  features  that  were  entirely  new  to  electri- 
cians. 

With  these  ideas  in  view  I  have  prepared  this 
little  volume.  It  is  not  intended,  in  the  slightest 
degree,  to  put  it  forward  as  a  scientific  work,  but  it 
will  probably  give  to  many  the  information  they 
desire  without  requiring  too  great  a  research  into 
books  which  treat  more  extensively  and  deeply  of  this 
subject. 

W.  H.  M. 

New  York,  May  1st,  1889. 


THE 

A  B  C  OF  ELECTRICITY. 


WE  now  obtain  so  many  of  our  comforts  and  con- 
veniences by  the  use  of  electricity,  that  all  young 
people  ouerht  to  learn  something  of  this  wonderful 
force,  in  order  to  understand  some  of  the  principles 
which  are  brought  into  practice. 

You  all  know  that  we  have  the  telegraph,  the  tele- 
phone, the  electric  light,  electric  motors  on  street 
cars,  electric  bells,  etc.,  besides  many  other  conven- 
iences which  the  use  of  electricity  gives  us. 

Every  one  knows  that,  by  the  laws  of  multiplica- 
tion, twice  two  makes  four,  and  that  twice  two  can 
never  make  anything  but  four.  Well,  these  useful 
inventions  have  been  made  by  applying  the  laws  of 
electricity  in  certain  ways,  just  as  well  known,  so  as 
to  enable  us  to  send  in  a  few  moments  a  message  to 
our  absent  friends  at  any  distance,  to  speak  with  them 
at  a  great  distance,  to  light  our  houses  and  streets 


8  THE  A  P>  C'OF  ELECTRICITY. 

,withi  cieetric:  light,  ;,a»n(i  to  do  many  other  useful 
things  with  quickness  and  ease. 

But  you  must  remember  that  we  do  not  know  what 
electricity  itself  really  is.  We  only  know  how  to  pro- 
duce it  by  certain  methods,  and  we  also  know  what 
we  can  do  with  it  when  we  have  obtained  it. 

In  this  little  book  we  will  try  to  explain  the  vari- 
ous ways  by  which  electricity  is  obtained,  and  how  it 
is  applied  to  produce  the  useful  results  that  we  see 
around  us. 

We  will  try  and  make  this  explanation  such  that  it 
will  encourage  many  of  you  to  study  this  very  imper- 
tant  and  interesting  subject  more  deeply. 

In  the  advanced  books  on  electricity  there  are 
many  technical  terms  which  are  somewhat  difficult 
to  understand,  but  in  this  book  it  will  only  be  neces- 
sary to  use  a  few  of  the  more  simple  ones,  which  it 
will  be  well  for  you  to  learn  and  understand  before 
going  further.  These  we  will  call. — 


THE  A  £  C  OF  ELECTRICITY. 


DEFINITIONS. 

The  three  first  measurements  in  electricity  are 
The  Volt, 
The  Ampere, 
The  Ohm. 

We  will  explain  these  in  their  order. 

THE  VOLT. — This  term  may  be  better  understood 
by  making  a  comparison  with  something  you  all 
know  of.  Suppose  we  have  a  tank  containing  100 
gallons  of  water,  and  we  want  to  discharge  it  through 
a  half  inch  pipe  at  the  bottom  of  the  tank.  Suppose, 
further,  that  we  wanted  to  make  the  water  spout 
upwards,  and  for  this  purpose  the  pipe  was  bent  up- 
wards as  in  figure  1. 

If  you  opened  the  tap  the 
water  would  spout  out  and 
upwards  as  in  figure  1. 

The  cause  of  its  spouting 
upwards  would  be  the 
weight  or  pressure  of  the 
water  in  the  tank.  This  u_  « 


10 


THE  ABC  OF  ELECTRICITY. 


pressure  is  reckoned  as  so  many  pounds  to  the  square 

inch  of  water. 

Now,  if  the  tank  were  placed 
on  the  roof  of  the  house  and 
the  pipe  brought  to  the  ground 
"^  f'  ;7  .  _  as  shown  in  figure  2,  the  water 
would  spout  up  very  much 
higher,  because  there  would  be 
many  more  pounds  of  pressure 
on  account  of  the  height  of  the 

i  m      pipce- 

DO,  you  see,  the  force  or  press- 
ure  of   water    is    measured   in 
pounds,  and,  therefore,  a  pound 
is  the  unit  of  pressure,  or  force 
Fig.  2.  °f  water.     Now,  in    electricit}r 

the  unit  of  pressure,  or  force,  is  called  a  volt. 

This  word,  "  Volt "  does  not  mean  any  weight,  as 
the  word  "  pound  "  weight  does.  You  all  know  that 
if  you  have  a  pound  of  water  you  must  have  some- 
tiling  to  hold  it,  because  it  has  weight,  and,  conse- 
quently, occupies  some  space.  But  electricity  itself 
has  no  weight  and  therefore  cannot  occupy  any 
space. 

When  we  desire  to  carry  water  into  a  house  or 
other  building,  we  do  so  by  means  of  hollow  pipes, 


THE  A  B  C  OF  ELECTRICITY.  H 

which  are  usually  made  of  iron.  This  is  the  way  that 
water  is  brought  into  houses  in  cities  and  towns,  so 
that  it  may  be  drawn  and  used  in  any  part  of  a  dwell- 
ing. Now,  the  principal  supply  usually  comes  from 
a  reservoir  which  ic  placed  up  on  high  ground  so  as 
to  give  the  necessary  pounds  of  pressure  to  force  the 
water  up  to  the  upper  part  of  the  houses.  If  some 
arrangement  of  this  kind  were  not  made,  we  could 
get  no  water  in  our  bedrooms,  because,  as  you  know, 
water  will  not  rise  above  its  own  level  unless  by 
force. 

The  water  cannot  escape  as  long  there  are  no  holes 
or  leaks  in  the  iron  pipes,  but  if  there  should  be  the 
slightest  crevice  in  them  the  water  will  run  out. 

In  electricity  we  find  similar  effects. 

The  electricity  is  carried  into  houses  by  means  of 
wires  which  are  covered,  or  insulated,  with  various 
substances,  such,  for  instance,  as  rubber.  Just  as  the 
iron  of  the  pipes  prevents  the  water  from  escaping, 
the  insulation  of  the  wire  prevents  the  escape  of  the 
electricity. 

Now,  if  we  were  to  cause  the  pounds  of  pressure 
of  water,  in  pipes  of  ordinary  thickness,  to  be  very 
greatly  increased,  the  pipes  could  not  stand  the  strain 
and  would  burst  and  the  water  escape.  So  it  is  with 
electricity.  If  there  were  too  many  volts  of  pressure, 


12  THE  A  B  C  OF  ELECTRICITY. 

the  insulation  would  not  be  sufficient  to  hold  it  and 
the  electricity  would  escape  through  the  covering,  or 
insulation,  of  the  wire. 

It  is  a  simple  and  easy  matter  to  stop  the  flow  of 
water  from  an  ordinary  faucet  by  placing  your  finger 
over  the  opening.  As  the  water  cannot  then  flow, 
your  finger  is  what  we  will  call  a  non-conductor  and 
the  water  will  be  retained  in  the  pipe. 

We  have  just  the  same  effects  in  electricity.  If  we 
pla^e  some  substance  which  is  practically  a  non- 
conductor, or  insulator,  such  as  rubber,  around  an 
electric  wire,  or  in  the  path  of  an  electric  current, 
the  el  ;<  Turicity,  acted  upon  by  the  volts  of  pressure, 
cannot  ese-ape,  because  the  insulation  keeps  it  from 
doing  so,  just  as  the  iron  of  the  pipe  keeps  the  water 
from  escaping.  Thus,  you  see,  the  volt  does  not  itself 
represent  electricity  but  only  the  pressure  which 
forces  it  through  the  wire. 

There  are  other  words  and  expressions  in  elec- 
tricity which  are  sometimes  used  in  connection  with 
the  word  "  Volt."  These  words  are  "  pressure  "  and 
"intensity."  We  might  say,  for  instance,  that  a  cer- 
tain dynamo  machine  had  an  electro-motive  force  of 
110  volts  ;  or  that  the  intensity  of  a  cell  of  battery 
was  2  volts,  etc.,  etc. 

We  might  mention,  as  another  analogy,  the  press- 


THE  A  B  C  OF  ELECTRICITY.  13 

ure  of  steam  in  a  boiler,  which  is  measured  or  cal- 
culated in  pounds,  just  as  the  pressure  of  water  is 
measured.  So,  we  might  say  that  100  pounds  steam 
pressure  used  through  the  medium  of  a  steam  engine 
to  drive  a  dynamo,  could  thus  be  changed  to  electric- 
ity at  100  volts  pressure. 

THE  AMPERE. — Now,  in  comparing  the  pounds 
pressure  of  water  with  the  volts  of  pressure  of  elec- 
tricity, we  used  as  an  illustration  a  tank  of  water 
containing  100  gallons,  and  we  saw  that  this 
water  had  a  downward  force  or  pressure  in  pounds. 
Let  us  now  see  what  this  pressure  was  acting 
upon. 

It  was  forcing  the  quantity  of  water  to  spout  up- 
wards through  the  end  of  the  pipe.  Now,  as  the 
quantity  of  water  was  100  gallons,  it  could  not  all 
be  forced  at  once  out  of  the  end  of  the  pipe.  The 
pounds  pressure  of  water  acting  on  the  100  gallons 
would  force  it  out  at  a  certain  rate,  which,  let  us  say, 
would  be  one  gallon  per  minute. 

This  would  be  the  rate  of  the  flow  of  water  out  of 
the  tank. 

Thus,  you  see,  we  find  a  second  measurement  to  be 
considered  in  discharging  the  water  tank.  The  first 
was  the  force,  or  pounds  of  pressure,  and  the  second 


14  THE  A  B  C  OF  ELECTRICITY. 

the  rate  at  which  the  quantity  of  water  was  being 
discharged  per  minute  by  that  pressure. 

This  second  measurement  teaches  us  that  a  certain 
quantity  will  pass  out  of  the  pipe  in  a  certain  time  if 
the  pressure  is  steady,  such  quantity  depending,  of 
course,  on  the  size  or  friction  resistance  of  the  pipe. 

In  electricity,  the  volts  of  pressure  act  so  as  to 
force  the  quantity  of  current  iv  flow  through  the  wires 
at  a  certain  rate  per  second,  and  the  rate  at  which  it 
flows  is  measured  in  amperes.  For  instance,  let  us 
suppose  that  an  electric  lamp  required  a  pressure  of 
100  volts  and  a  current  of  the  ampere  to  light  it  up, 
we  should  have  to  supply  a  current  of  electricity 
flowing  at  the  rate  of  one  ampere,  acted  upon  by  an 
electro-motive  force  of  100  volts. 

You  will  see,  therefore,  that  while  the  volt  does 
not  represent  any  electricity,  but  only  its  pressure, 
the  ampere  represents  the  rate  of  flow  of  the  current 
itself. 

You  should  remember  that  there  are  several  words 
sometimes  used  in  connection  with  the  word  "  am- 
pere," for  instance,  we  might  say  that  a  lamp  re- 
quired a  "  current "  of  one  ampere,  or  that  a  dynamo 
would  give  a  "  quantity  "  of  20  amperes. 

THE  OHM. — You  have  learned  that  the  pressure 


THE  A  B  C  OF  ELECTEICITY.  15 

would  discharge  the  quantity  of  water  at  a  certain 
rate  through  the  pipe.  Now,  suppose  we  were  to  fix 
two  discharge  pipes  to  the  tank,  the  water  would  run 
away  very  much  quicker,  would  it  not  ?  If  we  try 
to  find  a  reason  for  this,  we  shall  see  that  a  pipe  can 
only,  at  a  given  pressure,  admit  so  much  water 
through  it  at  a  time. 

Therefore,  you  see,  this  pipe  would  present  a  cer- 
tain amount  of  resistance  to  the  passage  of  the  total 
quantity  of  water,  and  would  only  allow  a  limited 
quantity  at  once  to  go  through.  But,  if  we  were  to 
attach  two  or  more  pipes  to  the  tank,  or  one  large 
pipe,  we  should  make  it  easier  for  the  water  to  flow, 
and,  therefore,  the  total  amount  of  resistance  to  the 
passage  of  the  water  would  be  very  much  less,  and 
the  tank  would  quickly  be  emptied. 

Now,  as  you  already  know,  water  has  substance 
and  weight  and  therefore  occupies  some  space,  but 
electricity  has  neither  substance  nor  weight,  and 
therefore  cannot  occupy  any  space  ;  consequently,  to 
carry  electricity  from  one  place  to  another  we  do  not 
need  to  use  a  pipe,  which  is  hollow,  but  we  use  a 
solid  wire. 

These  solid  wires  have  a  certain  amount  of  resist- 
ance to  the  passage  of  the  electricity,  just  as  the  water 
pipe  has  to  the  water,  and  (as  it  is  in  the  case  of  the 


16  THE  A  B  C  OF  ELECTRICITY. 

water),  the  effect  of  the  resistance  to  the  passage  of 
electricity  is  greater  if  you  pass  a  larger  quantity 
through  than  a  smaller  quantity. 

If  you  wanted  to  carry  a  quantity  of  electricity 
to  a  certain  distance,  and  for  that  purpose  used  a 
wire,  there  would  be  a  certain  amount  of  resistance 
in  that  wire  to  the  passage  of  the  current  through  it ; 
but  if  you  used  two  or  more  wires  of  the  same  size, 
or  one  large  wire,  the  resistance  would  be  very  much 
less  and  the  current  would*  flow  more  easily. 

Suppose,  that,  instead  of  emptying  the  water  tank 
from  the  roof  through  the  pipe,  we  had  just  turned 
the  tank  over  and  let  the  water  all  pour  out  at  once 
down  to  the  ground.  That  would  dispose  of  the 
water  very  quickly  and  by  a  short  way,  would  it  not  ? 
That  is  veiy  easy  to  be  seen,  because  there  would  be 
no  resistance  to  its  passage  to  the  ground. 

Well,  suppose  we  had  an  electric  battery  giving  a 
certain  quantity  of  current,  say  5  amperes,  and  we 
should  take  a  large  wire  that  would  offer  no  resist- 
ance to  that  quantity  and  put  it  from  one  side  of  the 
battery  to  the  other,  a  large  current  would  flow  at 
once  and  tend  to  exhaust  the  battery.  This  is  called 
a  short  circuit,  because  there  is  little  or  no  resistance, 
and  it  provides  the  current  with  an  easy  path  to 
escape.  Remember  this,  that  electricity  always  takes 


THE  A  B  C  OF  ELECTRICITY.  17 

the  easiest  path.  It  will  take  as  many  paths  as  are 
offered,  but  the  largest  quantity  will  always  take  the 
easiest. 

As  the  subject  of  resistance  is  one  of  the  most  im- 
portant in  electricity,  we  will  give  you  one  more  ex- 
ample, because  if  you  can  obtain  a  good  understand- 
ing of  this  principle  it  will  help  you  to  comprehend 
the  whole  subject  more  easily  in  your  future  studies. 

We  started  by  comparison  with  a  tank  holding  100 
gallons  of  water,  discharging  through  a  half-inch 
pipe,  and  showed  you  that  the  pounds  of  pressure 
would  force  the  quantity  of.  gallons  through  the  pipe. 
When  the  tap  was  first  opened,  the  water  would 
spout  up  very  high,  but  as  the  water  in  the  tank  be- 
came lower,  the  pressure  would  be  less,  and,  conse- 
quently, the  water  would  not  spout  so  high. 

So,  if  it  were  desired  to  keep  the  water  spouting 
up  to  the  height  it  started  with,  we  should  have  to 
keep  the  tank  full,  so  as  to  have  the  same  pounds  of 
pressure  all  the  time.  But,  if  we  wanted  the  water 
to  spout  still  higher,  we  should  have  to  use  other 
means,  such  as  a  force  pump,  to  obtain  a  greater 
pressure. 

Now,  if  we  should  use  too  many  pounds  pressure, 
it  would  force  the  quantity  of  water  more  rapidly 

through  the  pipe  and  would  cause  the  water  to  be- 

2 


18  THE  A  B  C  OF  ELECTRICITY. 

come  heated  because  of  the  resistance  of  the  pipe  to 
the  passage  of  that  quantity  acted  upon  by  so  great 
a  pressure. 

This  is  just  the  same  in  electricity,  except  that  the 
wire  itself  would  become  heated,  some  of  the  electric- 
ity being  turned  into  heat  and  lost.  If  a  wire  were 
too  small  for  the  volts  pressure  and  amperes  of  cur- 
rent of  electricity,  the  resistance  of  such  wire  would 
be  overcome,  and  it  would  become  red  hot  and  per- 
haps melt.  Electricians  are  therefore  very  careful 
to  calculate  the  resistance  of  the  wires  they  use  be- 
fore putting  them  up,  especially  when  they  are  for 
electric  lighting,  in  order  to  make  allowances  for  the 
amperes  of  current  to  flow  through  them,  so  that  but 
little  of  the  electricity  will  be  turned  into  heat  and 
thus  rendered  useless  for  their  purpose. 

The  Unit  of  resistance  is  called  the  OHM  (pro- 
nounced like  "  home  "  without  the  "  h  "). 

All  wires  have  a  certain  resistance  per  foot,  accord- 
ing to  the  nature  of  the  metal  used  and  the  size  of 
the  wire,  that  is  to  say,  the  finer  the  wire  the  greater 
number  of  ohms  resistance  it  has  to  the  foot. 

Water  and  Electricity  flow  under  very  similar 
conditions,  that  is  to  say,  each  of  them  must  have  a 
channel,  or  conductor,  and  each  of  them  requires 
pressure  to  force  it  onwards.  Water,  however,  being 


THE  A  B  C  OF  ELECTRICITY.  19 

a  tangible  substance,  requires  a  hollow  conductor ; 
while  electricity,  being  intangible,  will  flow  through 
a  solid  conductor.  The  iron  of  the  water  pipe  and 
the  insulation  of  the  electric  wire  serve  the  same 
purpose,  namely,  that  of  serving  to  prevent  escape  by 
reason  of  the  pressure  exerted. 

There  is  another  term  which  should  be  mentioned 
in  connection  with  resistance,  as  they  are  closely 
related,  and  that  is,  "  opposition"  There  is  no  gen- 
eral electrical  term  of  this  name,  but,  as  it  will  be 
most  easily  understood  from  the  meaning  of  the  word 
itself,  we  have  used  it. 

Let  us  give  an  example  of  what  opposition  would 
mean  if  applied  to  water.  Probably  every  one  knows 
that  a  water-wheel  is  a  wheel  having  large  blades,  or 
"  paddles  "  around  its  circumference. 

When  the  water,  in  trying  to  force  its  passage, 
rushes  against  one  of  these  paddles  it  meets  with  its 
opposition,  but  overcomes  it  by  pushing  the  paddle 
away.  This  brings  around  more  opposition  in  the 
shape  of  another  paddle,  which  the  water  also  pushes 
away.  And  so  this  goes  on,  the  water  overcoming 
this  opposition  and  turning  the  wheel  around,  by 
which  means  we  can  get  water  to  do  useful  work 
for  us. 

You  must  remember,  however,  that  it  is  only  by 


20  THE  A  B  C  OF  ELECTRICITY. 

putting  opposition  in  the  path  of   a  pressure   and 
quantity  of  water  that  we  can  get  this  work. 

The  same  principle  holds  good  in  electricity.  We 
make  electricity  in  different  ways,  and,  in  order  to 
obtain  useful  work,  we  put  in  its  path  the  instruments, 
lamps  or  machines,  which  offer  the  proper  amount  of 
resistance,  or  opposition,  to  its  passage,  and  thus 
obtain  from  this  wonderful  agent  the  work  we  desire 
to  have  done. 

You  have  learned  that  three  important  measure- 
ments in  electricity  are  as  follows  : 

The  Volt  is  the  practical  unit  of  measurement  of 
pressure  ; 

The  Ampere  is  the  practical  unit  of  measurement  of 
the  rate  of  flow  ; 
and 

The  Ohm  is  the  practical  unit  of  measurement  of 
resistance. 


THE  ABU  OF  ELECTRICITY.  21 


MAGNETISM. 

Now  we  will  try  to  explain  to  you  something 
about  magnets  and  magnetism.  There  are  very  few 
boys  who  have  not  seen  and  played  with  the  ordinary 
magnets,  shaped  like  a  horse-shoe,  which,  are  sold  in 
all  toy  stores  as  well  as  by  those  who  sell  electrical 
goods. 

Well,  you  know  that  these  magnets  will  attract 
and  hold  fast  anything  that  is  made  of  iron  or  steel, 
but  they  have  no  effect  on  brass,  copper,  zinc,  gold 
or  silver,  yet  there  is  nothing  that  you  can  see  which 
should  cause  any  such  effect.  You  will  notice,  then, 
that  magnetism  is  like  electricity ;  we  cannot  see  it, 
but  we  can  tell  that  it  exists  because  it  produces 
certain  effects.  And  here  is  another  curious  thing  ; 
magnetism  produces  electricity,  and  electricity  pro- 
duces magnetism.  This  seems  to  be  a  very  con- 
venient sort  of  a  family  affair,  and  it  is  owing  to 


22 


THE  A  B  C  OF  ELECTUICITY. 


this  close  relation  that  we  are  able  to  obtain  so  many 
wonderful  things  by  the  use  of  electricity. 

We  shall  now  show  you  how  electricity  produces 
magnetism,  and,  when  we  come  to  the  subject  of 
electric  lighting,  we  will  explain  how  magnetism  pro- 
duces electricity. 

The  easiest  way  to  show  how  electricity  makes 
magnetism  is  to  find  out  how  magnets  are  made. 
Suppose  we  wanted  to  make  a  horse-shoe  magnet, 
just  mentioned  above ;  we  would  take  a  piece  of 
steel,  and  wind  around  it  some  fine  copper  wire,  com- 
mencing on  one  leg  of  the  horse-shoe,  and  winding 
around  until  we  came  to  the  end  of  the  other  leg. 
Then  we  should  have  two  ends  of  wire  left,  as  shown 
in  the  sketch. 

We  connect  these  two 
ends  with  an  electric  bat- 
tery, giving,  say,  two 
volts,  and  then  the  am- 
p£res  of  current  of 
electricity  will  travel 
through  the  wire,  and 
in  doing  so,  has  such  an 
influence  on  the  steel, 
that  it  is  converted  into 
a  magnet,  such  as  you 


.  3. 


TflE  A  B  C  OF  ELECTRICITY.  23 

have  played  with.  The  current  is  "  broken,"  that  is 
to  say,  it  is  shut  off,  several  times  in  making  a  mag- 
net of  this  kind,  and  then  the  wire  is  taken  away 
from  the  battery  and  is  unwound  from  the  steel  horse- 
shoe, leaving  it  free  from  wire,  just  as  you  have  seen 
it.  This  horse-shoe  is  now  a  permanent  magnet,  that 
is,  it  will  always  attract  and  hold  pieces  of  iron  and 
steel. 

Now,  if  you  were  to  do  the  same  thing  with  a 
horse-shoe  made  of  soft  iron,  instead  of  steel,  it 
would  not  be  a  magnet  after  you  stopped  the  current 
of  electricity  from  going  through  the  wires,  al- 
though the  piece  of  iron  would  be  a  stronger  magnet 
while  the  electricity  was  going  through  the  wire 
around  it. 

The  steel  magnet  is  called  a  permanent  magnet, 
and  its  ends,  or  "poles,"  are  named  North  and 
South.  There  is  usually  a  loose  piece  of  steel  or 
iron,  called  an  "armature,"  put  across  the  ends, 
which  has  the  peculiar  property  of  keeping  the  mag- 
netism from  becoming  weaker,  and  thereby  retaining 
the  strength  of  the  magnet.  The  strongest  part  of 
the  magnet  is  at  the  poles,  while,  at '  the  point 
marked  +,  (which  is  called  the  neutral  point)  there 
is  scarcely  any  magnetism. 

It  will  be  well  to   remember   the   object   of   the 


24  THE  A  B  C  OF  ELECTRICITY. 

armature  as  we  shall  meet  it  again  in  describing 
dynamo  machines. 

The  magnets  made  of  iron 
are  called  electro-magnets,  be- 
cause they  exhibit  magnetism 
only  when  the  amperes  of  cur- 
rent of  electricity  are  flowing 
around  them.  They  also  have 
two  poles,  North  and  South, 
as  have  permanent  magnets. 
Electro-magnets  are  used  in 
.  4.  nearly  all  electrical  instru- 

ments, not  only  because  they  are-  stronger  than  per- 
manent magnets,  but  because  they  can  be  made  to  act 
instantly  by  passing  a  current  of  electricity  through 
them  at  the  most  convenient  moment,  as  you  will 
see  when  we  explain  some  of  the  electrical  instru- 
ments which  are  used  to  produce  certain  effects. 

Of  course,  there  are  a  great  many  different  shapes 
in  which  magnets  are  made.  The  simplest  is  the 
bar  magnet,  which  is  simply  a  flat  or  round  piece  of 
iron  or  steel.  Suppose  you  made  a  magnet  of  a  flat 
piece  of  steel,  and  put  on  top  of  it  a  sheet  of  paper, 
and  then  threw  on  the  paper  some  iron  filings,  you 
would  see  them  arrange  themselves  as  is  shown  in 
the  following  sketch. 


THE  A  B  C  OF  ELECTRICITY. 


25 


Fig.  5. 

The  filings  would  always  arrange  themselves  in 
this  shape,  no  matter  how  large  or  small  the  magnets 
were.  And,  if  you  were  to  cut  it  into  two  or  half  a 
dozen  pieces,  each  piece  would  have  the  same  effect. 
This  shows  you  that  each  piece  would  itself  become 
a  magnet  and  would  have  its  poles  exactly  as  the  large 
one  had. 

Now,  we  have  another  curious  thing  to  tell  you 
about  magnets.  If  you  present  the  North  pole  of  a 
magnet  to  the  South  pole  of  another  magnet,  they 
will  attract  and  hold  fast  to  each  other,  but  if  you 
present  a  South  pole  to  another  South  pole,  or  a 
North  pole  to  a  North  pole,  they  will  repel  each 
(Jther,  and  there  will  be  no  attraction.  You  can  per- 
form some  interesting  experiments  by  reason  of  this 
fact.  We  will  give  you  one  of  them. 


26  THE  A  B  C  OF  ELECTRICITY. 

Take,  say,  a  dozen  needles  and  draw  them  several 
times  in  the  same  direction  across  the  ends  of  a 
magnet  so  that  they  become  magnetized.  Now  stick 
each  needle  half  way  through  a  piece  of  cork,  and  put 
the  corks,  with  the  needles  sticking  through  them,  into 
a  bowl  of  water.  Then  take  a  bar  magnet  and  bring 
it  gradually  towards  the  middle  of  the  bowl  and  you 
will  see  the  corks  advance  or  back  away  from  the 
magnet.  If  the  ends  of  the  needles  sticking  up  out 
of  the  water  are  South  poles  and  the  end  of  the 
magnet  you  present  is  a  North  pole,  the  needles  will 
come  to  the  centre ;  but  will  go  to  the  side  of  the 
bowl  if  you  present  the  South  pole.  You  can  vary 
this  pretty  experiment  by  turning  up  the  other  ends 
of  part  of  the  needles. 

You  will  remember  that  when  we  explained  what 
"resistance"  meant,  we  told  you  that  electricity 
would  always  take  the  easiest  path,  and  while  part 
of  it  will  flow  in  a  small  wire,  the  largest  portion  will 
take  an  easier  path  if  it  can  get  to  something  larger 
that  is  a  metallic  substance.  Electricity  will  only 
flow  easily  through  anything  that  is  made  of  metal. 
You  will  also  remember  that  you  learned  that  when 
electricity  took  a  short  cut  to  get  away  from  its 
proper  path,  it  was  called  a  short  circuit. 

All  this  must  be  taken  into  consideration  when 


THE  A  B  C  OF  ELECTEICITY.  27 

magnets  are  being  made.  In  the  first  place,  the 
wire  we  wind  around  steel  or  iron  to  make  mag- 
nets must  always  be  covered  with  an  insulator  of 
electricit}r.  Magnet  wire  is  usually  covered  with 
cotton  or  silk.  If  it  were  left  bare,  each  turn  of  the 
wire  would  touch  the  next  turn  and  so  we  should 
make  such  an  easy  path  for  the  electricity  that  it 
would  all  go  back  to  the  battery  by  a  short  circuit, 
and  then  we  would  get  no  magnetic  effect  in  the  steel 
or  iron.  The  only  way  we  can  get  electricity  to  do 
useful  work  for  us  is  to  put  some  resistance  or  opposi- 
tion in  its  way.  So,  you  see,  that  if  we  make  it 
travel  through  the  wire  around  the  iron  or  steel, 
there  is  just  enough  resistance  or  opposition  in  its 
way  to  give  it  work  to  get  through  the  wire,  and 
this  work  produces  the  peculiar  effect  of  making  the 
iron  or  steel  magnetic. 

The  covering  on  the  wire,  as  yoy  will  remember,  is 
called   "  insulation." 


28  THE  A  B  C  OF  ELECTRICITY. 


THE  TELEGRAPH. 

EVERY  one  knows  how  very  convenient  the  tele- 
graph is,  but  there  are  not  many  who  think  how  won- 
derful it  is  that  we  can  send  a  message  in  a  few 
seconds  of  time  to  a  distant  place,  even  though  it 
were  thousands  of  miles  away.  And  yet,  though  the 
present  system  of  telegraphing  is  a  wonderful  one, 
the  method  of  sending  a  telegram  is  simple  enough. 
The  apparatus  that  is  used  in  sending  a  telegram  is 
as  follows : 

The  battery, 
The  wire, 
1'!:e  telegraph  key, 
The  sounder. 

The  different  kinds  of  electric  batteries  will  be 
mentioned  afterwards,  so  we  will  not  stop  now  to 
describe  them,  but  simply  state  that  a  battery  is  used 
to  produce  the  necessary  electricity.  As  you  all 
know  what  wire  is,  there  is  no  necessity  of  describing 
it  further. 


THE  A  B  C  OF  ELECTRICITY.  29 

The  telegraph  key  is  shown  in  the  sketch  below : 


Fig.  6. 

This  instrument  is  usually  made  of  brass,  except 
that  upon  the  handle  there  is  the  little  knob  which 
is  of  hard  rubber.  The  handle,  or  lever,  moves  down 
when  this  knob  is  pressed,  and  a  little  spring  beneath 
pushes  it  up  again  when  let  go.  You  will  see  a 
second  smaller  knob,  the  use  of  which  we  will  explain 
later. 

The  sounder  is  shown  below  : 


Fig.  7. 


30  THE  A  B  C  OF  ELECTRICITY. 

The  part  consisting  of  the  two  black  pillars  is  an 
electro-magnet,  and  across  the  top  of  these  pillars  is 
a  piece  of  iron,  called  the  "  armature,"  which  is  held 
up  by  a  spring. 

Now  let  us  see  how  the  battery  and  wire  are  placed 
in  connection  with  these  instruments.  You  have 
seen  that  we  usually  have  two  wires  for  the  electricity 
to  travel  in,  one  wire  for  it  to  leave  the  battery  and 
the  other  to  return  on.  But  you  will  easily  see  that 
if  two  wires  had  to  be  used  in  telegraphing,  it  would 
be  a  very  expensive  matter,  especially  when  they  had 
to  be  carried  thousands  of  miles.  So,  instead  of 
using  a  second  wire,  we  use  the  earth  to  carry  back 
the  electricity  to  the  battery,  because  the  earth  is  a  bet- 
ter conductor  even  than  wire.  Although  a  quantity  of 
earth,  equal  in  size  to  the  wire,  would  offer  thousands 
of  times  greater  resistance  than  the  wire,  yet  owing 
to  the  great  body  of  the  earth,  its  total  resistance  is 
even  less  than  any  telegraph  wire  used. 

When  two  electric  wires  are  run  from  a  battery 
and  connected  together  through  some  instrument, 
this  is  called  a  "  circuit,"  because  the  electricity  has 
a  path  in  which  it  can  travel  back  to  the  battery. 
This  would  be  a  "  metallic  "  circuit ;  but  when  one 
wire  only  is  used,  and  the  other  side  of  the  battery  is 
connected  with  the  earth,  it  is  called  a  "ground  "  or 


THE  A  B  C  OF  ELECTRICITY.  31 

"earth"    circuit,   because    the    electricity    returns 
through  the  earth. 

If  you  look  at  this  sketch  you  will  see  how  the 
telegraph  instruments  are  connected  and  will  then  be 
able  to  understand  how  a  message  can  be  sent. 


Here  we  have  two  sets  of  telegraph  apparatus,  one 
of  which,  let  us  say,  is  in  New  York  and  the  other 
in  Philadelphia. 

You  will  see  that  one  wire  from  the  battery  is  con- 
nected with  the  earth,  and  the  other  wire  with  the 
sounder.  Another  wire  goes  from  the  sounder  to 
one  leg  of  the  key  so  as  to  make  the  brass  base  of  the 
key  part  of  the  circuit.  The  other  leg  of  the  key  is 
"  insulated "  from  the  brass  base  by  being  separated 
therefrom  with  some  substance  which  will  not  carry 
electricity,  such,  for  instance,  as  hard  rubber. 

We  will  suppose   that  there  is  already  a  wire 


32  THE  A  B  C  OF  ELECTRICITY. 

strung  up  on  poles  between  New  York  and  Phila- 
delphia, and  that  the  key,  sounder  and  battery  in  the 
latter  city  are  connected  in  the  same  way  as  those  in 
New  York. 

Now,  to  enable  us  to  send  a  message  from  one  city 
to  the  other,  we  must  connect  the  ends  of  the  wire  to 
the  instruments  in  each  city ;  so  we  connect  one  end 
to  the  insulated  leg  of  the  key  in  New  York,  and  the 
other  end  to  the  insulated  leg  of  the  key  in  Phila- 
delphia. 

Everything  is  now  completed  and  as  soon  as  we 
find  out  what  is  the  use  of  that  part  of  the  key  that 
has  a  little  round  black  handle,  we  shall  be  ready  to 
start.  This  is  called  the  "  switch." 

If  you  will  look  once  more  at  the  picture  of  the  key 
you  will  see  under  the  long  handle  (or  lever)  a  little 
point  which  the  lever  will  touch  when  it  is  pressed 
down.  Now  this  little  point  is  part  of  that  insulated 
leg,  and,  therefore,  this  point  is  also  insulated  from 
the  base.  If  a  current  of  electricity  were  sent  along 
the  wire  it  could  not  get  any  further  than  this  point 
unless  we  put  in  some  arrangement  to  complete  the 
path,  or  circuit,  for  it  to  travel  in.  We,  therefore, 
put  in  the  switch. 

One  end  of  the  switch  (which  is  made  of  brass 
with  a  rubber  handle)  is  fastened  on  the  base  of  the 


THE  ABC  OF  ELECTRICITY.  33 

key,  so  that  it  may  be  moved  to  the  right  or  left. 
The  other  end,  when  the  switch  is  moved  to  the  left 
(or  "  closed  "),  touches  a  piece  of  brass  fastened  to 
the  little  point  we  have  mentioned,  and  so  makes  a 
free  path  for  the  electricity  to  go  through  the  base 
of  the  key  and  through  the  wire  to  the  sounder,  and 
from  there  to  the  battery  and  so  back  to  the  earth. 
This  switch  must  be  opened  before  the  sounder  near 
it  will  respond  to  its  neighboring  key. 

Now  we  are  ready  to  send  a  message.  Suppose  we 
want  to  send  a  telegram  from  New  York  to  Philadel- 
phia. The  operator  in  New  York  opens  his  switch 
and  presses  down  his  key  several  times.  The  switch 
on  the  Philadelphia  key  being  closed,  the  electricity 
goes  through  to  the  sounder  and  this  being  made  an 
electro-magnet  by  the  current  passing  through  the 
wire,  the  iron  armature  is  attracted  by  the  magnetism 
and  drawn  down  to  the  magnet  with  a  snap0  It  will 
stay  there  as  long  as  the  New  York  operator  keeps 
his  lever  pressed  down,  but,  when  he  allows  it  to 
spring  up,  there  is  no  current  passing  through  the 
Philadelphia  sounder  and  there  is  no  magnetism,  con- 
sequently the  armature  springs  up  again  with  a  click. 

As  often  as  the  operator  presses  down  his  key  lever 
and  lets  it  spring  up  again,  the  same  action  takes 

place  in  the  sounder,  and  it  makes  that  click,  click, 

3 


34  THE  A  It  C  OF  ELECTRICITY. 

which  you  have  heard  if  you  have  ever  seen  telegraph 
instruments  in  operation. 

Let  us  continue,  however,  to  send  our  message. 
The  New  York  operator,  having  pressed  down  his  key 
several  times  to  signal  the  Philadelphia  operator, 
closes  his  switch  to  receive  the  answer  from  Phila- 
delphia. The  operator  in  the  latter  city  then  opens 
his  switch  and  presses  down  his  key  several  times 
which  makes  the  New  York  sounder  click,  in  the 
same  way,  to  let  the  operator  there  know  that  he 
is  ready  to  receive  the  message.  He  then  closes  his 
switch  and  receives  the  telegram  which  the  New 
York  operator  sends  after  opening  his  key. 

Telegraphic  messages  are  sent  and  received  in  this 
way  and  are  read  by  the  sound  of  the  clicks. 

These  sounds  may  be  represented  on  paper  by  dots, 
dashes  and  spaces.  For  instance,  if  you  press  down 
the  key  and  let  it  spring  back  quickly,  that  would 
represent  a  dot.  If  you  press  down  the  key  and  hold 
it  a  little  longer  before  letting  it  spring  up  again,  it 
would  represent  a  dash.  A  space  would  be  represented 
by  waiting  a  little  while  before  pressing  down  the  key 
again. 

We  show  you  below  the  alphabet  in  these  dots, 
dashes  and  spaces,  and  these  are  the  ones  now  used 
in  sending  all  telegraphic  messages. 


THE  A  B  C  OF  ELECTRICITY.  35 

B  0  D         E         P  G 


H  I  J  K  L  M 

OP  Q  B  S         T 

•  •     •••••      mmmm     m  mm      «••      •§      •• 


V  W  X  Y  Z  ft 

••  ••       •••  •      •  ••§ 

Thus,  you  see,  if  you  were  telegraphing  the  word 
"  and  "  you  would  press  down  your  key  and  let  it 
return  quickly,  then  press  down  again  and  return 
after  a  longer  pause,  which  would  give  the  letter  A; 
then  slowly  and  quickly  which  would  be  N ;  then 
slowly  and  twice  quickly,  which  would  be  D. 

Any  persevering  boy  can  learn  to  operate  a  telegraph 
instrument  by  a  little  study  and  regular  practice ; 
and,  as  complete  learner's  sets  can  be  purchased  very 
cheaply,  this  affords  a  pleasant  and  useful  recreation 
for  boys. 

There  are  many  cases  where  two  boys  living  near 
each  other  have  a  set  of  telegraph  instruments  in 
their  homes  and  run  a  wire  from  one  house  to  the 
other,  thus  affording  many  hours  of  pleasant  and 
profitable  amusement. 


36  THE  A  B  C  OF  ELECTRICITY. 

In  giving  the  above  explanation  of  telegraphing 
we  have  described  only  the  simple  and  elementary 
form.  In  large  telegraph  lines,  such  as  those  of  the 
Western  Union,  there  are  many  more  additional  in- 
struments used,  which  are  very  complicated  and  diffi- 
cult to  understand;  such,  for  instance,  as  the  quad- 
ruplex,  by  which  four  distinct  messages  can  be  sent 
over  the  same  wire  at  the  same  time.  We  have, 
therefore,  described  only  the  simplest  form  in  order 
to  give  the  general  idea  of  the  working  of  the  tele- 
graph by  electro-magnetism,  which  is  the  principle  of 
all  telegraphing. 

When  you  study  electricity  more  deeply,  you  will 
find  this  subject  and  the  many  different  instruments 
very  interesting  and  wonderful. 


THE  A  J3  C  OF  ELECTRICITY* 


THE  TELEPHONE. 

You  probably  all  know  that  the  telephone  is  an 
electrical  instrument  by  which  one  person  may  talk 
to  another  who  is  at  a  distance  away.  Not  only  can 
we  talk  to  a  person  who  is  in  a  different  part  of  the 

* 

city,  but  such  great  improvements  have  been  made  in 
these  instruments  that  we  can  talk  through  the  tele- 
phone to  a  person  in  another  city,  even  though  it  be 
hundreds  of  miles  away. 

The  main  principle  of  the  telephone  is  electro- 
magnetism,  as  in  the  telegraph,  but  there  are  other 
important  points  in  addition  to  those  we  mentioned 
in  describing  the  latter. 

Let  us  take  first  the 

INDUCTION   COIL. 

You  will  remember  that  an  electro-magnet  is  made 
by  winding  many  turns  of  wire  around  a  piece  of  iron 
and  sending  a  current  of  electricity  through  this  wire. 

Now,  suppose  this  current  of  electricity  was  being 
supplied  by  two  cells  of  battery.  If  you  took  in  your 
hands  the  wires  coming  from  these  two  cells  giving, 
say,  four  volts,  you  could  not  feel  any  shock  ;  but  if 


38  THE  ABC  OF  ELECTRICITY 

you  were  to  take  hold  of  the  ends  of  the  wires  on 
the  electro-magnet  and  separate  them  while  this  same 
current  was  going  through,  you  would  get  a  decided 
shock. 

This  separation  would  "  break  "  the  circuit,  and 
the  reason  you  would  get  a  shock  is,  that  while  the 
electricity  is  acting  on  the  wire,  the  iron  itself  is 
magnetized  and  on  breaking  the  circuit  reacts  upon 
the  wire,  producing  for  a  moment  more  volts  of  press- 
ure in  every  turn  of  it.  Thus,  you  see,  this  weak 
pressure  of  electricity  as  it  travels  through  the  wire 
can  yet  produce,  through  its  magnetism,  strong 
momentary  effects,  but  you  cannot  feel  it  unless  you 
break  the  circuit. 

HOW  THE  INDUCTION  COIL  IS  MADE. 

The  object  of  the  induction  coil  is  to  produce  high 
intensity,  or  pressure,  from  a  comparatively  weak 
pressure  and  large  current  of  electricity ;  so,  if  we 
add  still  more  wire,  the  magnet  has  a  larger  number 
of  turns  to  act  upon  and  thus  makes  a  very  strong 
pressure,  or  large  number  of  volts,  but  a  lesser  num- 
ber of  amperes. 

Instead  of  taking  one  piece  of  iron,  as  we  would 
for  an  ordinary  electro-magnet,  we  take  a  bundle  of 
iron  wires  in  making  an  induction  coil,  as  these  give 
a  stronger  effect.  Around  this  bundle  of  wires  we 


THE  ABC  OF  ELECTRICITY.  89 

wrap  many  turns  of  insulated  copper  wire.  This  is 
called  the  primary  coil,  and  the  ends  of  this  wire  are 
to  be  attached  to  the  battery. 

On  top  of,  or  over,  this  primary  coil  we  wrap  a 
great  many  turns  of  very  fine  wire,  of  which,  as  it 
is  so  fine,  a  great  length  can  be  used.  This  is  called 
the  secondary  coil,  and  it  is  in  this  coil  that  the  volts, 
or  pressure,  of  electricity  become  strongest. 
We  show  you  a  sketch  of  an  induction  coil. 

At  the  left  hand  side 
of  the  cut  is  a  "  circuit 
breaker,"  which  is  sim- 
F  ply  a  piece  of  iron  (arma- 
ture) on  a  spring  placed 
opposite  the  iron  core. 
This  armature  is  made  a 
part  of  the  wire  leading  to  the  primary  coil.  When 
the  current  from  the  battery  is  sent  through  the 
wires,  the  core  becomes  magnetized  and  draws  this, 
armature  away  from  a  fixed  contact  point,  thus  break? 
ing  the  circuit,  but  the  spring  pulls  it  back,  again 
completing  the  circuit,  and  so  it  keeps  going  back 
and  forth  very  rapidly  with  a  br-r-r-ing  sound. 

If  you  were  now  to  take  hold  of  the  ends  of  the 
secondary  coil  you  would  get  a  continuous  series  of 
quick  shocks  which  would  feel  like  pins  and  needles 
running  into  you. 


40  THE  A  n  C  OF  ELECTRICITY. 

Perhaps  most  of  you  have  taken  hold  of  the  handles 
of  a  medical  battery  and  have  had  shocks  therefrom. 
In  so  doing,  you  have  simply  had  the  current  from 
the  secondary  of  an  induction  coil.  The  current  may 
be  made  weaker  by  sliding  a  metallic  cover  over  part 
of  the  iron  core  and  so  shutting  off  part  of  the  mag- 
netic effect. 

SPARKING  COILS. 

While  on  this  subject  we  may  add  that  these  coils 
will  produce  sparks  from  the  two  ends  of  the  wire  of 
the  secondary  coil.  These  sparks  vary  in  length 
according  to  the  amount  of  wire  in  this  coil.  -  Small 
ones  are  made  which  give  a  spark  a  quarter  of  an  inch 
in  length,  while  others  are  made  which  will  give 
sparks  10,  12,  and  16  inches  in  length.  In  the 
latter,  however,  there  are  many  miles  of  wire  in  the 
secondary  coil. 

The  largest  induction  coil  known  is  one  which  was 
made  for  an  English  scientist.  There  are  341,850 
turns,  or  280  miles,  of  wire  in  the  secondary  coil. 
With  30  cells  of  Grove  battery  this  coil  will  give  a 
spark  42  inches  in  length.  You  may  form  some  idea 
of  the  effect  of  this  induction  coil  when  we  state  that 
if  we  desired  to  produce  the  same  length  of  spark 
direct  from  batteries,  without  using  an  induction 
coil,  we  should  require  the  combined  volts  of  pressure 
of  60,000  to  100,000  cells  of  battery. 


THE  A  B  C  OF  ELECTRICITY.  41 

Having  explained  to  you  briefly,  the  induction 
coil, — how  it  is  made  and  its  action, — we  must  ask  you 
to  bear  these  principles  in  mind,  and  presently  we 
will  tell  you  how  it  is  used  in  the  telephone. 

The  next  thing  we  shall  try  to  explain  will  be 

THE  VIBRATING  DIAPHRAGM. 

Did  you  ever  take  the  end  of  a  cane  in  your  hand, 
raise  it  up  over  your  head,  and  then  bring  it  down 
suddenly  and  sharply,  so  that  it  nearly  touched  ths 
ground,  as  though  you  were  about  to  strike  some- 
tiling  ?  If  not,  try  it  now  with  a  thin  walking  cane 
or  with  a  pine  stick  about  three  feet  long  and  one  half 
inch  thick,  and  you  will  find  that  there  is  a  peculiar 
sound  given  out.  It  is  not  the  stick  that  makes  this 
sound  but  it  is  owing  to  the  fact  that  you  have  caused 
the  air  to  vibrate,  or  tremble,  and  thus  give  out  a 
sound. 

If  you  strike  a  tuning-fork,  sharply,  -you  will 
see  the  ends  vibrate  and  a  sound  will  be  given. 
If  you  put  your  fingers  on  top  of  a  silk  hat 
and  speak  near  it  you  will  feel  vibrations  of  your 
voice. 

Every  time  you  speak  you  cause  vibrations  of  the 
air  ;  and  the  louder  and  higher  you  speak  the  greater 
the  number  of  vibrations. 


42  THE  A  B  C  OF  ELECTRICITY. 

Suppose  you  take  a  thin  piece  of  wood  in  your  hands, 
(say  for  instance,  the  lid  of  a  cigar-box  cut  in  the 
shape  shown  in  the  picture), 
and  hold  it  about  two  inches  from 
your  mouth  and  then  speak.  You 
will  feel  the  wood  tremble  in  your 
hand.  This  is  because  the  vibra- 
tions of  the  air  cause  the  wood 
to  vibrate  in  the  same  manner. 
These  vibrations  are  very  minute 
and  cannot  be  seen  with  the  naked 
eye,  but  they  actually  take  place, 
iig.  10.  an(j  could  j^  measured  with  a 

delicately  balanced  instrument. 

Kow,  let  us  try  another  experiment  in  further  illus- 
tration of  this  principle.  We  will  take  a  tube  about 
three  inches  long  and  one  and  one-half  or  two  inches 
in  diameter.  This  tube  may  be  made  of  card-board. 
Now  cut  out  a  piece  of  thin  card-board  which  will 
just  fit  over  one  end  of  the  tube.  This  piece  we  will 
call  the  "diaphragm."  Fasten  the  diaphragm  by 
pasting  it  with  two  strips  of  thin  paper  to  the  tube. 
These  strips  of  paper  should  be  fastened  only  on  the 
ends,  and  the  middle  of  the  paper  allowed  to  be  slack, 
as  shown  in  the  picture,  so  that  the  diaphragm  may 
work  backwards  and  forwards  easily.  Take  a  small 


THE  A  B  C  OF  ELECTEICITY.  43 

shot  about  the  size  seen  in  the  sketch  and  tie  it  to  a 
single    thread   of   fine 
silk,  then  let  it  hang  as  . 

shown  in    the   sketch, 
so  that  it  will  only  just 
touch   the   diaphragm. 
Now,  if  you  speak  into 
the  open  end  of  the  tube 
the  diaphragm  will  vi- 
brate and  the  shot  will  "~  ^ 
be   seen  to     move    to                      Fig.  11. 
and  from  it  according  to  the  strength  of  the  vibra- 
tions.    If  we  could  by  any  means  make  a  diaphragm 
in  another  tube  reproduce  these  same  vibrations  we 
should  hear  the  same  words  re-spoken,  if  the  tube 
were  held  to  the  ear. 

While  the  vibrations  caused  by  the  human  voice 
are  too  minute  to  be  seen,  it  may  seem  surprising  that 
they  can  be  made  to  produce  power.  This  is  done 
by  an  ingenious  mechanicism  called  a  Phonomotor, 
perfected  by  the  great  inventor,  Thomas  A.  Edison, 
of  whom  every  one  has  probably  heard.  This  mechan- 
ism, when  spoken  or  sung  at  (or  into)  immediately 
responds  by  causing  a  wheel  to  revolve.  No  amount 
of  blowing  will  start  the  wheel,  but  it  can  instantly 
be  set  in  motion  by  the  vibrations  caused  by  sound. 


44 


THE  A  B  C  OF  ELECTRICITY. 


Fig.  12. 

The  Phonomotor,  (which  is  shown  in  the  engrav- 
ing) has  a  diaphragm  and  mouthpiece.  A  spring, 
which  is  secured  to  the  bed  piece,  rests  on  a  piece  of 
rubber  tubing  placed  against  the  diaphragm.  This 
spring  carries  a  pawl,  that  acts  on  a  ratchet  or 
roughened  wheel,  on  the  flywheel  shaft.  A  sound 
made  in  the  mouthpiece  creates  vibrations  in  the 
diaphragm ;  the  vibrations  of  the  diaphragm  move 
the  spring  and  pawl  with  the  same  impulses,  and  as 
the  pawl  thus  moves  back  and  forth  on  the  ratchet 
wheel,  it  is  made  to  revolve. 

The  instrument,  therefore,  is  of  great  value  for 
measuring  the  mechanical  force  of  sound  waves,  or 
vibrations,  produced  by  the  human  voice. 


THE  A  B  C  OF  ELECTRICITY. 
THE  TRANSMITTER. 


45 


That  part  of  the  telephone  into  which  we  speak  is 
called  the  transmitter.  This  is  usually  a  piece  of 
wood  having  a  round  mouthpiece  cut  through  it.  At 
the  other  side  of  this  mouthpiece  is  placed  a  dia- 
phragm made  of  a  thin  piece  of  metal,  which  is  held 
in  place  by  a  light  spring.  Behind  this  diaphragm, 
and  very  close  to  it,  is  placed  a  carbon  button.  Be- 
tween this  carbon  button  and  the  diaphragm  is  a 
small  piece  of  platinum,  which  is  placed  so  as  to 
touch  botli  the  button  and  diaphragm  very  lightly. 
This  platinum  contact  piece  is  connected  with  one  of 
the  wires  running  to  the  primary  of  the  induction 
coil,  and  the  spring  attached  to  the  carbon  button  is 
connected  with  the  battery  to  which  the  other  wire 
of  the  primary  is  connected.  This  is  all  shown  in 
the  sketch  of  a  transmitter  below  : 


P    D 


tO-  RECEIVER  OF  Tnt 
OTHER  TELEPHONE  i 


1 


Fig.  13. 

A,  is  the  mouthpiece ;  B,  the  diaphragm ;  C,  the 
carbon  button ;  D,  the  wire,  at  the  end  of  which  is 


46  THE  A  B  C  OF  ELECTRICITY. 

the  platinum  contact ;  E,  the  battery  and  F,  the  in- 
duction coil ;  P,  P,  are  the  wires  to  the  primary  and 
S,  S,  the  secondary  wires. 

We  will  now  say  a  few  words  about  the  receiver, 
and  then  describe  the  manner  in  which  the  telephone 
works. 

THE    RECEIVER. 

This  is  that  part  of  the  telephone  which  is  held  to 
the  ear,  and  by  which  we  can  hear  the  words  spoken 
into  the  transmitter  of  the  telephone  at  the  other  end 
of  the  line. 

The  receiver  is  made  of  hard  rubber,  and  contains 
a  permanent  bar  magnet,  which  is  wound  with  wire 
so  as  to  make  it  also  an  electro-magnet  when  desired. 
In  front  of  this  magnet  is  placed  loosely  a  diaphragm 
of  thin  sheet  iron.  This  diaphragm  is  placed  so  as  to 
be  within  the  influence  of  the  magnet,  but  just  so 
that  neither  one  can  touch  the  other. 


Fig.  14. 

The  above  is  a  sketch  of  the  receiver.     A,  and  B, 
are  the  wires  leading  to  the  magnet.    C,  and  D,  is  the 


THE  A  B  C  OF  ELECTRICITY.  47 

diaphragm.  E,  and  F,  are  where  the  wires  connect, 
one  from  the  secondary  of  the  induction  coil  in  the 
other  telephone,  and  the  other  connected  with  the 
earth. 

THE  CAIIBON  BUTTON. 

The  little  carbon  hutton  plays  an  important  part 
in  the  telephone.  You  will  see  from  the  sketch  of 
the  transmitter  that  the  current  of  electricity  will 
flow  through  the  carbon  button  to  the  contact  point 
and  through  the  wire  to  the  primary  of  the  induction 
coil. 

•  Now,  carbon  has  a  peculiarity,  which  is  this,  that 
if  we  press  this  carbon  button,  ever  so  slightly, 
against  the  platinum  contact,  there  would  be  less  re- 
sistance to  the  flow  of  the  electricity  through  the 
wire  to  the  primary,  and  the  more  we  press  it  the  less 
the  resistance  becomes.  The  consequence  of  this 
would  be  that  more  current  would  go  to  the  primary, 
and  the  secondary  would  become  correspondingly 
stronger.  If  the  carbon  button  were  left  untouched, 
and  nothing  pressed  against  it,  the  flow  of  current 
through  it  would  be  perfectly  even. 

Having  examined  the  inside  of  the  transmitter  and 
receiver,  and  understanding  the  effect  of  pressure  on 
the  carbon  button,  let  us  now  see 


48  THE  A  B  C  OF  ELECTRICITY. 

HOW  THE  TELEPHONE  WORKS. 

When  we  speak  into  the  mouthpiece  of  the  trans- 
mitter, the  vibrations  of  the  air  cause  the  diaphragm 
to  vibrate  very  rapidly,  and,  of  course,  every  move- 
ment of  the  diaphragm  presses  more  or  less  against 
the  carbon  button,  in  consequence  of  which  the  cur- 
rents passing  through  the  primary  of  the  induction 
coil  are  constantly  increased  and  diminished,  and 
thus  produce  similar  effects,  but  magnified,  in  the 
secondary. 

The  effect  of  this  is  that  the  magnet  in  the  receiver 
of  the  other  telephone  is  receiving  a  rapidly  changing 
current,  which,  producing  corresponding  magnetic 
changes,  makes  the  magnet  alternately  weaker  and 
stronger.  This  influences,  by  magnetism,  the  iron  dia- 
phragm accordingly  and  makes  it  reproduce  the  same 
vibrations  that  were  caused  by  the  speech  at  the  trans- 
mitter of  the  sending  telephone.  Thus,  the  same 
vibrations  being  reproduced,  the  original  sounds  are 
given  out,  and  we  can  hear  what  the  person  at  the 
sending  telephone  is  saying. 

The  action  of  the  telephone  illustrates  well  the 
wonderfully  quick  action  of  the  electric  current  by 
the  reproduction  of  these  sound  waves,  or  air  vibra- 
tions, for  they  number  many  thousands  in  one  min- 
ute's speech. 


THE  A  B  C  OF  ELECTRICITY.  49 


ELECTRIC  LIGHT. 

WE  have  now  arrived  at  a  very  interesting  part  of 
the  study  of  electricity,  as  well  as  a  more  difficult 
part  than  we  have  yet  told  you  of,  but  one  which  you 
can  easily  understand  if  you  read  carefully. 

You  must  all  have  seen  electric  lights,  either  in  the 
streets  or  in  some  large  buildings,  for  so  many  elec- 
tric lights  are  used  now,  that  there  are  very  few 
people  who  have  not  seen  them.  But  perhaps  some 
of  you  have  only  seen  the  large  dazzling  lights  that 
are  used  in  the  streets,  and  do  not  know  that  there  is 
another  kind  of  electric  light  which  is  in  a  globe 
about  the  size  and  shape  of  a  large  pear,  and  gives 
about  the  same  light  as  a  good  gas  jet. 

These  two  kinds  of  electric  lights  have  different 
names. 

The  large,  dazzling  lights  which  you  see  in  the 
streets  are  called  "  arc  lights,"  and  the  small  pear- 
shaped  lamps,  which  give  a  soft,  steady  light,  are 
called. "  incandescent  lights."  We  will  tell  you  later 
why  these  names  are  given  to  them. 

The  incandescent  lights  are  generally  used  in 
houses,  stores,  theatres,  factories,  steamboats  and 
other  places  where  a  number  of  small  lights  are  more 


50 


THE  A  B  C  OF  ELECTRICITY. 


Fig  15. 

pleasant  to  the  eyes.  The  arc  lights  are  used  to  light 
streets  and  large  spaces  where  a  great  quantity  of 
light  is  wanted. 

It  would  not  be  pleasant  to  have  one  of  these  daz- 
zling arc  lamps  in  your  parlor, — although  it  would  give 
a  great  deal  of  light, — because  your  eyes  would  soon 
become  tired.  But  two  or  three  of  the  small  incan- 
descent lights  would  be  very  agreeable,  because  they 
would  give  you  a  nice,  soft  light  to  read  or  work  by, 
and  would  not  tire  your  eyes.  So,  you  see,  these  two 


THE  A  B  C  OF  ELECTRICITY.  51 

A 


'   Fig.  16. 

different  kinds  of  lamps  are  very  useful  in  their 
proper  places. 

Now,  if  you  will  read  patiently  and  carefully, 
we  will  try  and  explain  how  both  these  lights  are 
made. 

You  have  seen  that  the  telegraph,  telephone,  elec- 
tric bells,  etc.,  are  worked  by  batteries.  Electric 
lights,  however,  require  such  a  large  amount  of  cur- 


52  THE  A  B  C  OF  ELECTRICITY. 

rent,  that  it  is  too  expensive  to  produce  them  in  large 
quantities  by  batteries.  A  small  number  of  lamps 
could  be  lighted  by  batteries,  but  if  we  were  to  at- 
tempt to  use  them  to  light  500  or  1,000  lamps  to- 
gether, the  expense  would  be  so  enormous  as  to  make 
it  entirely  out  of  the  question. 

There  are  over  one  and  a  half  millions  of  incan- 
descent lamps  in  use  in  the  United  States,  but  you 
will  easily  see  that  there  could  not  be  that  number 
used  if  we  had  to  depend  on  batteries  to  light  them. 
You  will  understand  this  more  thoroughly  when  you 
have  finished  reading  this  little  book. 

Well,  you  will  ask,  if  we  cannot  use  batteries,  what 
is  used  to  produce  these  electric  lights  ? 

Machines,  called  "  dynamo-electric  machines,"  or 
"  dynamos,"  which  are  driven  by  steam  engines  or 
water-power,  are  used  to  produce  the  electricity  which 
makes  these  lamps  give  us  light. 

You  will  remember  that  in  the  chapter  on  Mag- 
netism we  explained  to  you  how  electricity  makes 
magnetism,  and  now  we  will  explain  how,  in  the 
dynamo,  magnetism  makes  electricity. 

It  has  been  found  that  the  influence  of  a  magnet 
is  very  strong  at  its  poles,  and  that  this  influence  is 
always  in  the  same  lines.  This  influence  has  been 
described  as  "lines  of  force,"  which  you  will  see 


THE  A  B  C  OF  ELECT1UCITY. 


represented  in  the  sketch  below,  by  the  dotted  lines. 
Of  course,  these  lines  of  force  are  only  imaginary 
and  cannot  be  seen  in  any 
magnet,  but  they  are  always 
present.      The   meaning   of 
this  term  "  lines  of  force  " 
then,  is  used  to  designate  the 
strength  of  the  magnet. 

Many  years  ago  the  great 
scientist,  Faraday,  made  the 
discovery,  that,  by  passing  a 
closed  loop  of  wire  through 
the  magnetic  lines  of  force 
existing  between  the  poles  of 
a  magnet,  the  magnetism  pro- 
duced the  peculiar  effect  of 
creating  a  current  of  electric- 
ity in  the  wire.  If  the  closed  loop  of  wire  were  passed 
down,  say  from  U  to  D,  the  current  flowed  in  the 
wire  in  one  direction,  and  if  it  were  passed  upwards, 
from  D  to  U,  the  current  flowed  in  the  other  direc- 
tion. Thus,  you  see,  magnetism  produces  electric- 
ity in  the  closed  loop  of  wire  as  it  cuts  through  the 
magnetic  lines  of  force.  Just  why  or  how,  nobody 
knows ;  we  only  know  that  electricity  is  produced  in 
that  way,  and  to-day  we  make  practical  use  of  this 


D 
Fig.  17. 


54  THE  A  n  C  OF  ELECTRICITY. 

method  of  producing  it  by  embodying  this  principle 
in  dynamo  machines,  as  we  will  shortly  explain. 

In  carrying  this  discovery  into  practice  in  making 
dynamo-machines  we  use  copper  wire.  If  iron  were 
used,  there  would  be  a  current  of  electricity  generated, 
but  it  would  be  much  less  in  quantity,  because  iron 
wire  has  much  greater  resistance  to  the  passage  of 
electricity  than  the  same  size  of  copper  wire. 

Perhaps  you  can  understand  it  more  thoroughly  if 
we  state  that  when  a  closed  loop  of  wire  is  passed  up 
and  down  between  the  poles  of  a  strong  magnet  there 
is  a  very  perceptible  opposition  felt  to  the  passage  of 
the  wire  to  and  fro. 

This  is  due  to  the  influence  of  the  magnetism  upon 
the  current  produced  in  the  wire  as  it  cuts  through 
the  lines  of  force,  and,  inasmuch  as  these  lines  of 
force  are  always  present  at  the  poles  of  a  magnet,  you 
will  see  that  no  matter  how  many  times  you  pass  the 
loop  of  wire  up  and  down,  there  will  be  created  in  it 
a  current  of  electricity  by  its  passage  through  the 
lines  of  force. 

Suppose,  that  instead  of  using  one  single  loop  of 
copper  wire,  you  wound  upon  a  spool  a  long  piece  of 
wire  like  this 


THE  A  B  C  OF  ELECTRICITY.  55 


Fig,  18. 

and  that  you  turned  this  spool  around  rapidly 
between  the  poles  of  the  magnet,  you  would  be 
cutting  the  lines  of  force  by  the  same  wire  a  great 
many  times,  and  every  time  one  length  of  the  wire 
cut  through  the  lines  of  force  some  electricity  would 
be  generated  in  it,  and  this  would  continue  as  long 
as  the  spool  was  revolved.  But,  as  each  length  would 
only  be  a  part  of  the  one  piece  of  wire,  you  will 
easily  see  that  there  would  be  a  great  deal  of  elec- 
tricity generated  in  the  whole  piece  of  wire. 

All  we  have  to  do  then,  is  to  collect  this  electricity 
from  the  two  ends  of  the  wire,  and  use  it.  If  we 
should  attach  two  wires  to  the  two  ends  of  this  wire  on 
the  spool,  they  would  be  broken  off  when  it  turned 
around,  so  we  must  use  some  other  method,  We  fix 
on  the  end  of  the  spool  (which  is  called  an  "  arma- 
ture ")  two  pieces  of  copper,  so  that  they  will  not 
touch  each  other,  thus  : 


f 


Fig.  19. 


56  THE  A  B  C  OF  ELECTRICITY. 

and  fasten  the  ends  of  the  wire  to  these  pieces 
of  copper.  This  is  called  a  "  commutator "  and, 
as  you  see,  is  really  the  ends  of  the  wire  on 
the  spool.  Now  we  get  two  thin  flat  pieces  of 
copper  and  fix  them  so  that  they  will  rest  upon 
the  copper  bars  of  the  commutator  but  will  not 
go  round  with  it.  These  two  flat  pieces  of  cop- 
per are  called  the  "  brushes  ",  and  they  will  collect 
from  the  commutator  the  electricity  which  is  gathered 
in  the  wire  around  the  spool.  As  the  brushes  stand 
still,  two  wires  can  be  fastened  to  them,  and  thus, 
the  amperes  of  current  of  electricity,  acted  upon  by 
the  volts  pressure,  can  be  carried  away  to  be  used  in 
the  lamps,  for  you  must  remember  that  as  long  as 
the  spool  turns  around,  it  gathers  more  electricity 
while  there  is  any  magnetism  for  the  wire  on  the 
spool  to  pass  through.  The  constant  revolving  of  the 
spool  creates  so  much  electricity  that  it  is  driven  out 
from  the  wire  on  the  spool,  through  the  commutator 
to  the  brushes,  and  there  it  finds  a  path  to  travel  away 
from  the  pressure  of  the  new  electricity  which  is  all 
the  time  being  made. 

In  this  way  we  got  a  continuous  current  of  elec- 
tricity in  the  two  wires  leading  from  the  commutator, 
and  can  use  it  to  light  electric  lamps  or  for  other  use 
ful  purposes. 


THE  A  B  C  OF  ELECTRICITY.  57 

In  explaining  this  to  you,  so  far,  we  have  used  as 
an  illustration  of  the  magnet  one  of  the  steel  perma- 
nent magnets  in  order  to  make  the  explanation  more 
simple,  but  now  that  you  understand  how  the  elec- 
tricity is  made,  we  must  explain  to  you  something 
about  the  magnets  that  are  used  in  dynamo-machines. 
We  can  perhaps  make  this  more  clear  by  giving 
another  example. 

Suppose  you  had  a  dynamo  which  was  lighting  up 
100  of  the  incandescent  lamps,  each  of  200  ohms 
resistance  and  each  requiring  100  volts  pressure. 
Now  each  lamp  would  take  just  a  certain  quantity  of 
electricity,  say,  half  an  ampere ;  so,  the  100  lamps 
would  require  one  hundred  times  that  quantity. 
But,  if  you  turned  off  50  of  these  lamps  at  once,  the 
tendency  would  be  for  the  pressure  to  rise  above  the 
100  volts  required  for  the  other  50,  and  they  would 
be  apt  to  burn  out  quicker.  It  is  plainly  to  be  seen 
then,  that  we  must  have  some  means  of  regulating 
the  magnetism  so  as  to  regulate  the  lines  of  force  for 
the  wire  on  the  armature  to  cut  through.  We  can 
do  this  with  an  electro-magnet  but  not  with  a  per- 
manent magnet,  because  we  cannot  easily  regulate 
the  amount  of  magnetism  which  a  permanent  magnet 
will  give. 

There  is  another  reason  why  we  cannot  use  per- 


58  THE  A  n  c  OF  ELECTRICITY. 

manent  magnets  in  a  dynamo,  and  that  is,  because 
they  cannot  be  made  to  give  as  much  magnetism  as  an 
electro-magnet  will  give. 

Thus  you  will  see  that  there  are  very  good 
reasons  for  using  electro-magnets  in  making  dynamo- 
machines.  Let  us  see  now  how  these  electro-magnets 
and  dynamos  are  made,  and  then  examine  the 
methods  which  are  followed  to  operate  and  use 
them. 

You  must  remember,  to  begin  with,  that  in  refer- 
ring to  wire  used  on  magnets  and  armatures  and  for 
carrying  the  electricity  away  to  the  lamps,  we  al- 
ways mean  wire  that  is  covered  or  insulated.  In 
electric  lighting,  insulated  wire  is  always  used,  ex- 
cept at  the  points  where  it  is  connected  with  the 
dynamo,  the  lamps,  a  switch,  or  any  point  where  we 
make  what  is  called  a  "  connection." 

As  the  shape  of  the  magnets  is  different  in  the 
dynamos  of  various  inventors,  we  will  take  for  illus- 
tration the  one  that  is  nearest  the  shape  of  the  horse- 
shoe and  the  shape  that  is  generally  used  in  illustrat- 
ing the  principle  of  the  dynamo.  This  is  the  form 
used  by  Mr,  Edison,  whom  we  have  previously  men 
tioned.  This  form  is  shown  in  the  sketch  below. 


THE  A  B  C  OF  ELECTRICITY. 


Fig.  20. 

Now,  although  this  magnet  appears  to  be  in  one 

piece  it  really  consists  of  five  parts  screwed  together 
so  as  to  make,  practically,  one  piece.  The  names  of 
the  parts  are  as  follows  ;  F,,  F,  are  the  "  cores  "  ;  C, 
the  "  yoke,"  which  binds  them  together,  and  P,  P, 
the  "  Pole  pieces,"  where  the  magnetism  is  the 
strongest.  These  pole  pieces  are  rounded  out  to  re- 
ceive the  armature,  which,  as  you  will  remember,  is 
the  part  that  turns  around. 

The  cores,  F,  F,  are  first  wound  with  a  certain 
amount  of  wire,  which  depends  upon  the  use  the 
dynamo  is  to  be  made  for.  Thus,  you  will  see,  there 
will  be  on  each  core  two  loose  ends  of  the  wire  that 
is  wound  around  it,  namely,  the  beginning  of  the 
wire  and  the  end  where  we  leave  off  winding,  which 


60  THE  A  B  C  OF  ELECTRICITY. 

on  the  two  cores  together  will  make  four  ends  of 
wire.  We  will  tell  you  presently  what  is  done  with 
them. 

After  the  cores  are  wound,  they  are  screwed  firmly 
to  the  yoke  and  to  the  pole  pieces  so  as  to  make,  for 
all  practical  purposes,  one  whole  piece  pretty  nearly 
the  shape  of  a  horse-shoe  magnet. 

Now,  to  make  the  dynamo  complete,  we  must  put 
in  the  armature  between  the  poles,  which  are 
rounded  off,  as  you  will  see,  to  accommodate  it.  The 
armature  is  held  up  by  two  "  bearings  "  which  you 
will  see  in  the  sketch  of  the  complete  dynamo 
below. 


THE  A  B  C  OF  ELECTRICITY.  61 

The  armature  in  a  practical  dynamo  machine  con- 
sists of  a  large  spool  made  of  thin  sheets  of  iron 
firmly  fastened  together  and  having  a  steel  shaft  run 
through  the  centre,  upon  which  it  revolves. 

Tliis  spool,  or  armature,  is  wound  with  a  number 
of  strands  of  copper  wire.  The  commutator,  instead 
of  consisting  of  two  bars,  is  made  in  many  dynamos 
with  as  many  bars  as  there  are  strands  of  wire,  and 
the  ends  of  these  wires  are  fastened  to  the  bars  of  the 
commutator  so  as  to  make,  practically,  one  long  piece 
of  wire  just  as  we  showed  you  in  explaining  how  the 
electricity  was  produced. 

The  brushes,  resting  upon  the  commutator,  carry 
away  the  electricity  from  it  into  the  wires  with 
which  they  are  connected. 

Now  we  have  our  dynamo  all  put  together  and 
ready  to  start  as  soon  as  we  properly  connect  these 
four  loose  ends  of  wire  on  the  cores. 

If  you  will  turn  back  to  figure  20,  you  will  see 
that  two  of  the  wires  are  marked  I  and  the  other  two 
O.  The  letter  I  means  the  inside  wire,  or  where 
the  winding  began,  and  the  letter  O  means  the  out- 
side wire,  or  where  we  left  off  winding. 

Now,  if  we  fasten  together  (or  "  connect ")  the 
two  ends  of  wires,  I  and  O,  near  the  top  of  the  mag- 
net, we  make  the  two  wires  round  the  cores  into  one 


62  THE  A  B  C  OF  ELECTRICITY. 

wire,  which  starts,  say  at  I  near  the  poles,  goes  all 
around  one  core  crosses  over  and  around  the  other 
core  down  to  the  other  end  of  the  wire  to  O  near  the 
poles. 

So  far  we  have  called  the  iron  a  magnet,  although 
it  is  not  a  magnet  until  electricity  is  put  into  it,  so, 
when  the  dynamo  is  started  for  the  first  time,  these 
two  ends  of  wire,  I  and  O,  are  connected  to  a  battery 
for  the  purpose  of  sending  electricity  through  the 
wire  on  the  cores.  When  the  electricity  goes  into 
this  wire  the  iron  immediately  becomes  a  magnet 
and  the  lines  of  force  are  present  at  the  poles. 

Now,  the  armature  is  turned  around  rapidly  by  a 
steam  engine  and,  as  the  wire  on  the  armature  cuts 
the  lines  of  force  with  great  rapidity  and  so  fre- 
quently, there  is  quickly  generated  a  large  quantity 
of  electricity,  which  passes  out  as  fast  as  it  is  made, 
through  the  commutator  and  the  brushes  to  the  lamp. 
And  so  long  as  the  armature  is  revolved  and  the 
battery  attached,  the  electricity  will  be  made,  or  as 
it  is  usually  termed,  "  generated." 

As  we  stated  above,  a  battery  is  used  the  first  time 
the  dynamo  is  run,  and  now  we  will  explain  why  it 
is  not  needed  afterwards. 

Although  iron  will  not  become  a  permanent 
magnet,  like  steel,  it  does  not  lose  all  its  magnetism 


THE  A  B  C  OF  ELECTRICITY.  63 

after  it  has  been  once  thoroughly  charged.  When 
the  dynamo  is  stopped,  after  the  first  trial,  and  the 
battery  is  taken  away,  you  will  discover  only  traces 
of  magnetism  about  the  poles.  They  will  not  readily 
attract  even  a  needle  or  iron  filings ;  but  there  is, 
nevertheless,  a  very  small  amount  of  magnetism  left 
in  the  iron.  Small  as  this  magnetism  is,  however,  it 
is  enough  to  make  very  faint  and  weak  lines  of  force 
at  the  poles  of  the  magnet. 

After  the  battery  is  taken  away,  the  ends  of  the 
wire  on  the  cores,  which  were  connected  to  the  bat- 
tery, are  connected,  instead,  to  the  wires  which  carry 
away  the  electricity  from  the  brushes  to  the  lamps. 
Thus,  you  will  see,  if  any  electricity  goes  from  the 
dynamo  to  the  lamps,  part  of  it  must  also  find  its  way 
through  the  wires  which  are  around  the  cores. 

We  will  now  start  up  the  dynamo  without  having 
any  battery  attached  and  see  what  happens.  The 
armature  turns  around  and  the  wires  upon  it  cut 
through  those  very  faint  lines  of  force  which  are 
always  a.t  the  poles.  This,  as  you  know,  makes  some 
electricity ;  very  little,  to  be  sure,  but  it  comes  out 
through  the  brushes  to  the  wires  leading  to  the  lamps, 
and  there  it  finds  the  wires  leading  back  to  the  cores. 
Well,  part  of  this  weak  current  of  electricity  goes 
into  these  wires  and  travels  back  round  the  cores  and 


64  THE  A  13  C  OF  ELECTRICITY. 

so  makes  the  magnetism  stronger.  The  consequence 
of  this  is  that  the  lines  of  force  become  stronger  and, 
as  the  armature  keeps  turning  around,  the  electricity 
naturally  becomes  stronger  and  so  there  is  more  of  it 
going  through  the  wires  back  to  the  cores  and  in- 
creasing the  strength  of  the  magnet  all  the  time, 
until  the  dynamo  becomes  strong  enough  to  generate 
all  the  current  it  was  intended  to  give  for  the  lamps. 

Of  course,  you  understand  that  the  stronger  the 
magnet  becomes,  the  greater  will  be  the  lines  of  force 
and  the  greater  the  amount  of  electricity  made  by 
the  turning  of  the  armature.  Now,  there  is  naturally 
a  limit  to  what  can  be  done  with  any  particular  dy- 
namo, so,  while  the  electricity  continues  to  strengthen 
the  magnetism  and  the  magnetism  increases  the 
electricity,  this  cannot  go  beyond  what  is  called  the 
"  saturation  "  point  of  the  magnet. 

Saturation  means  that  the  iron  is  full  of  magnetism, 
and  will  hold  that  much  but  no  more.  You  will 
learn  more  as  to  the  saturation  of  magnets  when  you 
study  electricity  more  deeply,  and  we  therefore  do 
not  intend  to  enter  into  that  subject  in  this  book. 
We  will  only  state,  however,  that  the  magnets  of 
dynamos  are  not  always  charged  up  to  their  satura- 
tion point. 


THE  A  B  C  OF  ELECTRICITY. 


65 


THE  LAMPS. 

So  far  you  have  learned  how  the  current  of  electric- 
ity is  produced,  and  now  we  will  follow  along  the 
wires  to  find  out  how  it  makes  the  lamps  give  out 
both  strong  lights  and  the  smaller  pleasant  ones. 

Suppose  we  take  first  the  large  dazzling  lights  we 
see  in  the  streets,  which,  as  you  know,  are  called 

ARC  LIGHTS. 

Those  who  have  seen  the  arc  lamps  will  readily 
recognize  them  from  this  picture. 

You  will  see  that  there  are  two 
sticks  or  "  pencils  "  or  carbon.  Now 
you  will  remember  that  in  the  chapter 
on  Magnetism  we  told  you  that  in 
order  to  have  electricity  do  ivork  for  us 
we  must  put  some  resistance  or  opposi- 
tion in  its  way.  When  we  get  light 
from  an  electric  lamp  it  is  because 
we  make  the  electricity  do  some 
work  in  the  lamp,  and  this  work  is 
in  pushing  its  way  through  a  resist- 
ance or  opposition  which  is  in  the 
lamp. 

When  we  generate  electricity  in 
the  dynamo  and  put  two  wires  for 

5 


Kg.  22. 


G6  THE  A  B  C  OF  ELECTRICITY. 

it  to  travel  in,  the  current  goes  away  from  the 
dynamo  through  one  of  the  wires  and  will  go  back 
to  the  dynamo  through  the  other  one  if  it  can 
possibly  get  a  chance  to  get  to  this  other  one. 
Now,  the  electricity  which  is  constantly  being  made 
fills  the  wires  and  acts  as  a  pressure  to  force  the  cur- 
rent through  the  wires  back  to  the  dynamo,  and,  if  we 
put  no  resistance  or  opposition  in  the  way,  it  would 
have  a  very  easy  path  to  travel  in  and  would  do  no 
work  at  all.  The  wires  leading  to  an  electric  lamp 
should  have  very  little  resistance,  not  sufficient  to 
require  any  work  from  the  current  in  passing 
through. 

So,  if  we  bring  the  two  carbons  in  an  arc  lamp  to- 
gether they  really  form  part  of  the  wire  and  do  not 
interrupt  the  current  in  its  travels,  but,  if  we  separate 
the  carbons,  we  make  a  gap  which  the  current  must 
jump  across  if  it  wants  to  go  on.  As  the  volts,  or 
pressure,  is  so  great,  the  current  must  jump,  and  this 
against  the  resistance  or  opposition  in  an  arc  lamp,  is 
that  which  gives  the  current  so  much  work  to  do. 
Indeed,  so  hard  is  it  for  the  current  to  jump  across 
this  gap  that  it  breaks  off  from  one  carbon  a  shower 
of  tiny  particles  as  fine  as  the  finest  dust,  and 
makes  them  white  hot  in  passing  to  the  other.  This 
shower  of  fine  carbon  dust,  together  with  the  ends  of 


THE  A  B  G  OF  ELECTRICITY.  67 

the  carbon,  being  white  hot,  of  course  makes  a  light 
and  this  is  the  dazzling  light  which  you  see  in  the  arc 
lamp. 

Of  course,  when  the  electricity  has  jumped  over 
from  one  carbon  to  the  other,  it  goes  through  it  to 
the  wire,  and  so  passes  on  to  the  next  lamp,  where  it 
has  to  jump  again,  and  so  on  until  it  has  gone  through 
the  last  lamp,  then  it  has  an  easy  path  to  get  back  to 
the  dynamo. 

Now,  we  want  you  to  understand  more  thoroughly 
how  that  much  resistance  or  opposition  will  cause 
heat,  so  we  will  try  to  give  you  a  simple  example. 

Most  of  you  know  that  if  you  were  holding  a  rope 
tightly  in  your  hands  and  some  one  pulled  it  through 
them  quickly  and  suddenly,  it  would  get  very  hot 
and  your  hands  would  feel  as  though  they  were  be- 
ing burned.  This  is  heat  caused  by  your  hands 
resisting  or  opposing  the  passage  of  the  rope  through 
them,  and  if  you  could  hold  on  tightly  enough  and 
the  rope  was  drawn  through  quickly  enough,  it  would 
take  fire.  This  fire  would,  therefore  cause  heat  and 
light. 

It  is  just  this  principle  of  resistance  to  the  passage 
of  the  current  which  causes  the  light  in  an  arc  lamp, 
as  we  have  shown  you. 


68  THE  A  B  C  OF  ELECTRICITY. 

INCANDESCENT   LAMPS. 

You  have  just  learned  that  the  light  in  an  arc  lamp 
is  caused  by  the  current  forcing  off  from  the  carbon 
sticks  tiny  particles  and  heating  them  up  until  they 
give  a  brilliant  light.  So,  you  see,  in  an  arc  light 
there  is  a  wearing  away  of  carbon  by  electricity,  and, 
therefore,  these  sticks,  or  pencils,  of  carbon  in  time 
are  all  burned  away.  In  practice,  the  carbon  pencils 
last  about  8  or  10  hours,  and  then  new  ones  must  be 
put  in. 

Now,  in  the  incandescent  lamp  there  is  also  carbon 
used,  but  the  light  is  not  produced  by  the  combustion 
or  wasting  away  of  the  carbon,  as  we  will  show  you. 

The  picture  on  next  page  will  show  you  the  appear- 
ance of  an  incandescent  lamp. 


THE  A  13  C  OF  ELECTRICITY. 


69 


Pig.  23. 

EDISON  INCANDESCENT  LAMP, 

You  will  see  that  this  lamp  consists  of  a  pear-shaped 
globe,  and  inside  is  a  long  U-shaped  strip  of  carbon 
only  a  little  thicker  than  an  ordinary  thread.  This  is 
a  strip  of  bamboo  cane  which  has  been  carbonized  to 
a  thread  of  charcoal.  It  is  joined  to  two  wires  which 
come  through  the  glass.  These  two  wires  come  down 
through  the  bottom  of  the  globe,  and  one  is  fastened 


70  THE  A  B  C  OF  ELECTRICITY. 

to  a  brass  screw  ring,  while  the  other  wire  is  fastened 
to  a  brass  button  at  the  bottom  of  the  lamp.  These 
two  (the  ring  and  button)  must,  as  you  know,  be 
separated  from  each  other  by  something  which  will 
not  cany  electricity,  or  they  would  make  a  short  cir- 
cuit when  the  electricity  was  applied.  We  separate 
the  ring  and  the  button  by  Plaster  of  Paris. 

Now,  if  we  took  the  ends  of  two  wires  which  were 
charged- with  the  proper  amount  of  electricity  and  put 
one  wire  on  the  screw  ring,  and  the  other  on  the 
button,  the  lamp  would  light  up,  because  there  would 
be  a  complete  path  for  the  current  to  travel  in. 

It  will,  however,  be  plain  to  you  that  it  would  be 
awkward  to  light  the  lamps  in  this  way,  so  we  use  a 
"socket"  into  which  the  lamp  is  screwed. 

The  wires  from  the 
dynamo  carrying  the 
electricity,  are  connected 
in  the  socket,  one  wire 
to  the  screw  thread 
into  which  the  screw 
ring  fits  and  the  other 
to  a  button  which  the 

__  button      on      the     lamp 

Fie*  24 

touches  when   the  lamp 

is  screwed  into   the  socket.     Thus   we  have  a  con- 


THE  A  B  C  OF  ELECTRICITY.  71 

nected  path  for  the  current  to  travel  in,  or,  as  it  is 
termed,  a  complete  circuit. 

You  will  notice  that  in  the  incandescent  lamp  the 
electricity  does  not  need  to  jump,  as  it  does  in  the  arc 
light,  because  we  give  it  one  continuous  straight  line 
to  travel  in. 

In  order,  however,  to  get  the  current  to  do  work 
for  us,  we  put  some  resistance  in  its  path,  which  it 
must  overcome  in  order  to  travel  back  to  the  dynamo. 
The  resistance,  in  an  incandescent  lamp,  is  the  U- 
shaped  carbon  strip  (or,  as  it  is  called,  "filament"). 
This  charcoal  filament  has  so  much  greater  resistance 
than  the  wires,  that  it  opposes,  or  resists,  the  passage 
of  the  electricity  through  it ;  but  the  electricity  must 
go  through,  and  as  it  is  strong  enough  to  force  its 
way,  it  overcomes  this  resistance  and  passes  on 
through  the  carbon  to  the  wire  at  the  other  end. 
You  see  it  is  a  struggle  between  the  carbon  and  the 
electricity,  the  current  being  determined  to  go  on 
and  the  carbon  trying  to  keep  it  back ;  and,  in  the 
end,  the  electricity,  being  the  stronger,  gets  the  best 
of  it ;  but  the  struggle  has  been  so  hard  that  the  car- 
bon has  been  raised  to  a  white  heat,  and  so  gives  out  a 
beautiful  light,  which  continues  as  long  as  the  current 
of  electricity  flows. 

You  will  remember  that  in  the  arc  light  the  carbon 


72  THE  A  B  C  OF  ELECTRICITY. 

is  slowly  consumed  and  new  ones  must  be  put  in.  If 
the  carbon  in  the  incandescent  light  were  consumed 
it  would  not  last  many  minutes,  because  it  is  only 
about  the  size  of  a  horsehair.  Now,  you  will  natu- 
rally inquire  why  this  fine  strip  is  not  burned  up 
when  it  is  raised  to  so  high  a  heat.  Well,  we  will 
tell  you. 

You  know  that  if  you  light  a  match  and  let  it  burn, 
the  wood  will  all  be  consumed.  But  did  you  ever 
light  a  match,  put  it  into  a  small  bottle  and  put  the 
cork  in  ?  If  you  never  did,  do  so  now  as  an  experi- 
ment, and  you  will  see  that  the  match  will  keep 
lighted  for  an  instant  and  then  go  out  without  con- 
suming the  wood. 

The  reasons  for  this  are  very  simple.  In  order  to 
burn  anything  up  entirely  it  is  absolutely  necessary 
to  have  the  gas  called  oxygen  present,  and,  as  the 
air  you  live  in  contains  a  very  large  amount  of 
oxygen,  there  is  more  than  sufficient  in  your  room  to 
cause  the  wood  of  the  match  to  be  entirely  consumed 
after  it  is  lighted.  But  there  is  such  a  small  quan- 
tity of  oxygen  in  the  bottle  that  it  is  not  enough  to 
keep  the  fire  going  in  the  match,  and,  consequently, 
it  will  not  burn  up  the  wood. 

The  reason  the  charcoal  filament  in  an  incandes- 
cent lamp  is  not  burned  up  is  because  there  is  no 


THE  A  B  C  OF  ELECTRICITY.  73 

oxygen  inside  the  globe.  After  the  carbon  is  put  in 
its  place  all  the  oxygen  is  drawn  out  through  a  tube, 
and  the  glass  is  sealed  up  so  that  no  more  oxygen 
can  get  in.  This  is  called  obtaining  a  "  vacuum," 
and  vacuum  means  a  space  without  air. 

There  being  no  oxygen  in  the  globe,  it  is  impos- 
sible for  the  carbon  to  burn  up  ;  so,  the  incandescent 
lamp  will  continue  to  give  its  light  for  a  very  long 
time,  some  of  them  lasting  for  thousands  of  hours. 
Some  day,  however,  from  a  great  variety  of  obscure 
causes,  the  carbon  becomes  weak  in  some  particular 
spot  and  breaks,  and  the  light  ceases.  When  this 
happens,  we  unscrew  the  lamp  and  put  another  one 
in,  and  the  light  goes  on  as  usual. 

Now  you  have  learned  how  the  incandescent  lamp 
is  made  to  give  light.  We  will  add  that  it  is  a 
beautiful,  soft,  white  light,  almost  without  heat,  it 
will  not  explode,  throws  off  no  poisonous  fumes  like 
gas  or  oil  lamps,  and  has  many  other  points  of  com- 
fort and  convenience  which  make  it  very  desirable. 

ELECTRIC   LIGHT   WIRES. 

Before  closing  the  subject  of  electric  light  you 
would  perhaps  like  to  know  something  about  the 
way  in  which  we  place  the  wires  leading  to  the  lamps. 

If  you  remember  what  we  told  you  about  measure- 
ments in  the  beginning  of  this  book  it  will  be  easy 
to  understand  what  follows : — 


74 


THE  A  B  C  OF  ELECTRICITY. 


You  know  that  if  you  have  a  very  great  pressure, 
you  can  force  a  quantity  through  a  small  conductor. 
This  is  the  principle  upon  which  the  arc  lamps  are 
run.  Every  arc  lamp  takes  about  40  to  50  volts  and 
from  5  to  10  amperes  to  produce  the  light,  and  they 
are  connected  with  the  wires  as  shown  below ; 


{  J 


Fig.  28. 


THE  A  B  C  OF  ELECTRICITY.  75 

This  is  called'  running  lamps  in  "  series,"  and,  as 
you  will  see  from  the  sketch,  the  wire  starts  out  from 
the  dynamo  and  connects  to  one  carbon  of  the  first 
arc  lamp,  and  to  the  other  carbon  is  connected 
another  wire  which  goes  on  the  next  lamp,  and  so 
on  until  the  last  lamp  is  reached  and  then  the  wire 
goes  back  to  the  dynamo.  This  forms,  practically, 
one  continuous  loop  from  one  brush  to  the  other  of 
the  dynamo. 

The  current  starts  out,  makes  its  way  through  the 
first  lamp,  goes  on  to  the  next,  makes  its  way  through 
that,  and  so  on  till  it  has  jumped  the  last  one,  then  it 
goes  back  to  the  dynamo. 

Now,  as  each  of  these  jumps  requires  a  pressure  of 
40  or  50  volts,  you  will  easily  see  that  the  total  pressure, 
in  volts,  of  the  electricity  must  be  as  many  times  40 
or  50  volts  as  there  are  lamps  to  be  lighted ;  so,  if 
there  were  60  lamps  in  circuit,  there  would  be  2,400 
to  3,000  volts  pressure,  which,  while  it  gives  very 
fine  lights,  might  cause  instant  death  to  anyone 
touching  the  wires. 

Suppose  anything  happened  to  the  first  lamp, 
which  stopped  the  current  from  jumping  through  it  ? 
There  would  be  no  path  for  the  current  to  travel 
further,  and,  consequently,  all  the  lights  would  go 
out.  To  get  over  this  difficulty  there  is  sometimes 


76  THE  A  B  C  OF  ELECTRICITY. 

used  what  is  called  a  "  shunt,"  which  only  acts  whei? 
the  lamp  will  not  light.  This  shunt  carries  the  cur- 
rent round  the  lamp  to  the  other  wire,  so  that  it  may 
travel  on  and  light  up  the  other  lamps. 

WIRES  FOR  INCANDESCENT  LAMPS. 

The  wiring  for  incandescent  lamps  is  carried  out 
in  an  entirely  different  way,  which  you  can  see  by 
comparing  the  sketch  on  the  next  page  with  the  one 
showing  the  wiring  for  arc  lamps. 


THE  A  B  C  OF  ELECTEICITY. 


77 


Fig.  26. 

This  is  called  connecting  in  "  multiple  arc." 

You  will  notice  that  the  two  wires  running  out 

from  the  dynamo  (which  are  called  the  main  wires), 

do  not  form  one  continuous  loop  as  in  the  arc  light 

system,  but  that  a  smaller  wire  is  attached  to  one  of 


78  THE  A  B  C  OF  ELECTRICITY. 

the  main  wires  and  then  connected  to  the  screw  ring 
in  the  lamp  socket;  then  another  wire  is  connected 
to  the  button  in  the  socket  and  afterwards  to  the 
other  main  wire.  Thus,  every  lamp  forms  an  inde- 
pendent path  through  which  the  current  can  travel 
back  to  the  dynamo. 

Now  if  we  turn  one  of  these  incandescent  lamps 
out,  we  simply  shut  off  one  of  these  paths  and  the 
electricity  travels  through  the  other  lamps,  and,  if  we 
wish,  we  can  turn  out  all  the  lamps  but  one  and 
there  will  still  be  a  way  for  the  electricity  to  go  back 
to  the  dynamo. 

In  the  arc  lamps  we  must  have  a  very  high  num- 
ber of  volts  pressure,  because  the  electricity  has  only 
one  path,  and  it  all  has  to  pass  through  the  first  and 
other  lamps  till  it  comes  to  the  last  one.  In  the  in- 
candescent light  the  electricity  has  as  many  paths  as 
there  are  lamps,  so  we  only  need  to  keep  one  certain 
pressure  in  volts  in  the  main  wires  all  the  time.  This 
pressure  is  even  all  the  way  through  the  main  wires, 
and,  therefore,  it  is  ready  to  light  a  lamp  the  instant 
it  is  turned  on,  because,  as  you  have  seen,  electricity 
will  always  get  back  to  the  dynamo  if  there  is  a  pos- 
sible chance,  and  the  lamp  opens  a  path. 

The  volts  pressure  used  to  operate  any  number  of 
incandescent  lamps  is  altogether  very  much  less  than 


THE  A  B  C  OF  ELECTRICITY.  79 

for  a  number  of  arc  lights.  For  example,  in  the 
Edison  system,  the  pressure  (sometimes  called 
"  Electro-motive  force  "),  is  only  about  110  volts, 
which  is  very  mild  and  not  at  all  dangerous.  This 
electro-motive  force  would  be  the  same  if  there  were 
one  lamp  or  ten  thousand  lighted. 

While  this  Edison  current  would  not  hurt  anyone, 
you  should  remember  that  it  is  much  the  better  plan 
not  to  touch  any  electric  light  wires  until  you  have 
learned  a  great  deal  more  on  this  subject. 

We  may  add  that  each  of  the  standard  incandes- 
cent lamps  requires  only  about  one-half  to  three- 
quarters  of  an  ampere  of  current  to  make  them  give 
a  light  of  16-candle  power,  which  is  about  the  light 
given  by  a  very  good  gas  jet,  and  while  the  electro- 
motive force,  or  pressure,  would  only  be  about  110 
volts,  whether  there  were  one  lamp  or  ten  thousand 
lighted,  there  must  be  sufficient  amperes  in  the  wires 
to  give  Teach  lamp  its  proper  quantity. 

SWITCHES. 

We  have  made  mention  several  times  of  turning  on 
or  off  one  or  more  lights,  and  nowT  perhaps,  you 
would  like  to  know  how  this  is  done. 

Suppose    the  electricity    was   traveling    through 


80 


THE  A  B  C  OF  ELECTRICITY. 


wires  to  one  or  several  lamps,  it  would  light  up  those 
lamps  as  long  as  the  wires  provided  a  path  to  travel 
in,  but  if  you  were  to  cut  one  of  them,  which  is 
called  "breaking  the  circuit,"  there  would  be  no 
road  for  the  electricity  to  follow,  and,  consequently, 
its  course  would  be  stopped  short  and  the  lamps 
would  go  out.  You  will  remember  that  electricity 
must  have  a  complete  circuit  or  it  can  do  no  work,  and 
in  electric  lighting  it  is  always  a  metallic  circuit  that 
is  used. 

Now,  the  switch  is  simply  an  article  which  is  used 
to  break  the  circuit  so  that  the  current  cannot  pass 
on.  The  simplest  form  of  switch  is  as  seen  in  the 
sketch. 


Circuit 


Closed 


Wire 


\Vir» 


Fig.  27. 

You  will  see  that  there  is  a  wire  cut  in  two,  and  to 
one  piece  is  attached  a  metallic  piece,  A,  which  turns 
one  way  or  the  other,  and  when  it  is  turned  so  as  to 
touch  the  other  part  of  the  wire,  the  circuit  is  closed 
and  the  electricity  goes  from  the  lower  part  of  the 
wire  through  the  metallic  piece  A,  to  the  other  part 


THE  A  13  C  OF  ELECTRICITY.  81 

of  the  wire,  thus  making  a  complete  circuit  or  path 
for  the  electricity  to  travel  in. 

If  we  turn  the  piece,  A,  away  from  the  upper  wire 
this  breaks  the  circuit  and  cuts  off  the  path,  and,  of 
course,  the  lamps  would  go  out. 

This  is  the  principle  of  the  switch,  and,  although 
they  are  made  in  thousands  of  ways,  switches  all  have 
the  same  object,  namely,  the  closing  and  breaking  of 
the  circuit,  whether  it  is  for  one  or  a  hundred 
lamps. 

WIRE  ON  DYNAMOS. 

In  explaining  to  you  the  construction  and  working 
of  dynamo  machines,  we  did  not  state  anything  about 
the  amounts  of  wire  used  in  winding  the  machine. 

It  is  not  our  intention  to  say  exactly  how  much  is 
used  on  any  one  dynamo,  because  that  is  among  the 
things  you  will  have  to  learn  when  you  come  to  study 
the  subject  of  electricity  more  deeply. 

We  simply  want  to  have  you  understand  that  upon 
the  number  of  turns  of  wire  on  any  one  machine  de- 
pends the  effect  that  that  amount  of  wire,  carrying 
electricity,  will  have  upon  a  certain  weight  of  iron 
when  the  armature  is  revolved  a  certain  number  of 
turns  per  minute. 

A  certain  number  of  strands  of  wire  on  an  armature 

will  only  do  a  certain  amount  of  work,  at  the  most, 

6 


82  THE  A  B  C  OF  ELECTRICITY. 

so,  you  will  see  that  a  small  dynamo  will  not  produce 
as  much  electricity  as  a  larger  one  containing  more 
iron  and  wire.  For  high  pressure  there  must  be 
more  strands  of  wire  cutting  the  lines  of  force  more 
frequently  than  would  be  required  for  low  pressure  ; 
and,  to  produce  a  great  many  amperes,  the  armature 
must  be  larger  and  the  wire  upon  it  thicker  than  it 
would  need  to  be  if  only  a  small  number  of  amperes 
were  wanted. 

This  of  itself  is  a  very  deep  and  complicated 
subject,  and  many  books  have  been  written  upon  it 
alone.  We  shall,  therefore,  not  attempt  to  go  more 
deeply  into  it  in  this  little  book,  but  simply  content 
ourselves  with  giving  you  the  general  idea,  which 
will  be  sufficient  until  you  make  a  thorough  study  of 
the  subject. 


THE  A  B  C  OF  ELECTRICITY.  83 


ELECTRIC  POWER. 

ONE  of  the  most  convenient  uses  to  which  elec- 
tricity is  put  is  in  producing  motive  power  for  driv- 
ing all  kinds  of  machines,  from  a  sewing  machine  to  a 
railway  train,  and  we  will  now  try  to  explain  how  we 
can  get  this  kind  of  work  from  electricity. 

To  begin  with,  you  all  know  that  a  piece  of  ma- 
chinery is  usually  made  to  work  by  revolving  a  wheel 
which  is  part  of  the  machine,  either  by  means  of  a 
steam  engine,  or  by  water  power,  or,  as  a  sewing  ma- 
chine, by  foot  power.  Now  when  we  work  a  piece  of 
machinery  by  electricity  we  do  just  the  same  thing, 
by  using,  instead  of  the  steam  engine,  or  water,  or 
foot  power,  an  electric  engine  called  an  "  electro- 
motor," which  operates  in  the  same  way,  namely,  by 
turning  the  wheel  of  the  machine  it  is  applied  to. 

Foot  power  is  hard  work  for  the  person  who  is 
applying  the  power,  and,  as  you  can  easily  see,  one 
person  can  make  only  a  very  little  power  by  use  of 
the  feet.  Steam  and  water  power  can  be  used  for 


84  THE  A  B  C  OF  ELECTRICITY. 

any  large  amount  of  work,  but  the  work  must  be  with- 
in a  few  hundred  feet  of  the  engine  or  the  power 
cannot  be  used. 

If  there  were  a  factory  using  steam  power  a  block 
or  two  away  from  where  you  lived,  and  you  had  a 
lathe  in  your  house  which  you  would  like  to  have  run 
by  the  steam  power  in  the  factory,  it  would  be  prac- 
tically impossible  to  do  this.  Now,  if  the  factory 
were  still  further  away  from  your  house,  it  would  be 
still  more  impossible,  and  if  it  were  a  mile  away,  it 
would  be  foolish  to  dream  of  taking  steam  power  from 
a  place  so  far  away. 

Suppose,  however,  that  this  factory  was  lighted  by 
electric  lights,  it  would  be  a  very  easy  matter  to  take 
some  of  the  power  over  to  your  house.  This  could 
be  done,  even  if  the  factory  were  miles  away,  by 
taking  two  wires  from  their  electric  light  wires  and 
running  them  into  your  house  to  an  electro-motor 
connected  with  your  lathe.  This  electro-motor  would 
then  run  your  lathe  just  as  well  as  if  it  were  belted  to 
a  steam  engine. 

So,  you  see,  power  can  be  carried  in  the  form 
of  electricity  through  two  wires  over  very  great 
distances  and  made  to  do  work  at  a  long  way  from 
the  engine  which  is  turning  the  dynamo  to  make  the 
electricity.  Thus,  you  may  have  brought  into  your 


THE  A  11  C  OF  ELECTRICITY.  85 

house  wires  which  will  give  lights  and,  at  the  same 
time,  power  to  run  a  sewing  machine,  a  lathe,  or  any 
other  piece  of  machinery. 

Having  learned  so  far,  that  a  dynamo  will  make  a 
continuous  current  of  electricity,  and  that  two  wires 
will  carry  this  current  to  any  place  where  it  is 
wanted ;  let  us  now  see  what  takes  place  in  the 
electro-motor  to  transform  the  electricity  into  power. 

An  electro-motor  (which  we  will  now  call  by  its 
short  name,  Motor),  is  simply  a  machine  made  like  a 
dynamo.  Curious  as  it  may  seem  to  you,  it  is  a  fact, 
that  if  you  take  two  dynamo  machines,  exactly  alike, 
and  run  one  with  the  steam  engine  so  as  to  produce 
electricity  and  then  take  the  two  main  wires  and  at- 
tach them  to  the  brushes  of  the  other  dynamo,  the 
electricity  will  drive  this  other  dynamo  so  as  to  pro- 
duce a  great  deal  of  power  which  could  be  used  for 
driving  other  machines.  Thus,  the  second  dynamo 
would  become  a  motor. 

In  the  chapter  on  dynamos  we  explained  something 
about  the  way  they  were  made,  and  how  the  electric- 
ity was  produced. 

THE  MOTOR. 

You  will  remember  that  the  armature  consists  of  a 
spool  wound  with  wire.  This  spool  is  made  of  iron 


86  THE  ABC  OF  ELECTRICITY. 

plates  fastened  together  so  as  to  form  one  solid  piece. 
The  armature  of  a  motor  may  be  made  in  the  same 
way,  in  fact,  the  whole  motor  is  practically  a  dynamo 
machine. 

There  is  something  more  about  magnetism  which 
we  will  tell  you  of  here,  because  you  will  more  easily 
understand  it  in  its  relation  to  an  electro-motor. 

If  we  take  an  ordinary  piece  of  iron  and  bring  one 
end  of  it  near  to  (but  not  touching)  one  pole  of  a 
magnet,  this  piece  of  iron  will  itself  become  a  weaker 
magnet  as  long  as  it  remains  in  this  position.  This 
is  said  to  be  magnetism  by  "  induction."  The  end 
of  the  piece  of  iron  nearest  to  the  magnet  will  be  of 
the  opposite  polarity.  For  instance,  if  the  pole  of 
the  magnet  were  North,  the  end  of  the  iron  which  was 
nearest  to  this  North  pole  would  be  South  and  of 
course  the  other  end-  would  be  North.  To  make  this 
more  plain  we  show  it  in  the  sketch  below. 


THE  A  B  C  OF  ELECTRICITY. 


Steel  Permanent  Magnet.  Iron. 

Fig.  28. 

This  would  be  the  same  whether  the  magnet  were 
a  permanent  or  electro-magnet. 

You  will  remember  also  that  the  North  pole  of  one 
magnet  will  attract  the  South  pole  of  another  magnet, 
but  will  repel  a  North  pole. 

These  are  the  principles  made  use  of  in  an  electro- 
motor, and  we  will  now  try  to  show  you  how  this  is 
carried  into  practice. 

Although  a  motor  is  made  like  a  dynamo,  we  will 
show  a  different  form  of  machine  than  the  dynamo 
already  illustrated,  because  it  will  help  you  to  under- 
stand more  easily. 


88 


THE  A  B  C  OF  ELECTRICITY. 


Fig.  29. 

Here  we  have  an  electro-magnet  with  its  poles,  and 
an  iron  armature  wound  with  wire,  just  as  in  the 
dynamo  we  have  described,  except  that  its  form  is 
different. 

A  commutator  and  brushes  are  also  used,  but  the 
electricity,  instead  of  being  taken  away  from  the 
brushes,  is  taken  to  them  by  the  wires  connected  with 
them.  Two  wires  are  also  connected  which  take 
part  of  the  electricity  around  the  magnet,  just  as  in 
the  dynamo. 

Now,  when  the  volts  pressure  and  amperes  of 
electricity  coming  from  a  dynamo  or  battery  are 
turned  into  the  wires  leading  to  the  brushes  of  the 
motor,  they  go  through  the  commutator  into  the 
armature  and  round  the  magnet,  and  so  create  the 


THE  A  B  C  OF  ELECTRICITY. 


89 


Hues  of  force  at  the  poles  and  magnetize  the  iron  of 

the  armature. 

Let  us  see  what  the  effect  of  this  is. 

The  poles  of  the  magnet  "become  North  and  South, 
and  the  four  ends  on  the  armature  also  become  North 
and  South,  two  of  each. 

By  referring  to  the  sketch  again,  we  shall  see  what 
takes  place. 


.  30, 

The  North  pole  of  the  magnet  is  doing  two  things  ; 

it  is  repelling,  or  forcing  away,  the  upper  North  pole 
of  the  armature  and  at  the  same  time  drawing 
towards  itself  the  lower  South  pole  of  the  armature. 
In  the  mean  time,  the  South  pole  of  the  magnet  is 
repelling  the  South  pole  of  the  armature  and  at  the 
same  time  drawing  towards  itself  the  North  pole  of 
the  armature. 


90  THE  A  B  C  OF  ELECTRICITY. 

This,  of  course,  makes  the  armature  turn  around, 
and  the  same  poles  are  again  presented  to  the  mag- 
net, when  they  are  acted  upon  in  the  same  manner, 
which  makes  the  armature  revolve  again,  and  this 
action  continues  as  long  as  electricity  is  brought 
through  the  wires  to  the  brushes.  Thus,  the  arma- 
ture turns  around  with  great  speed  and  strength,  and 
will  then  drive  a  machine  to  which  it  is  attached. 

The  speed  and  strength  of  the  motor  are  regulated 
by  the  amount  of  iron  and  wire  upon  it.  and  by  the 
volts  pressure  and  amperes  of  electricity  supplied  to 
the  brushes.  Motors  are  made  from  a  small  size  that 
will  run  a  sewing  machine  up  to  a  size  large  enough 
to  run  a  railway  train,  and  are  often  operated  through 
wires  at  a  great  distance  from  the  place  where  the 
electricity  is  being  made,  sometimes  miles  awa}^. 

They  are  also  made  in  a  great  many  different 
forms,  but  the  principle  is  practically  the  same  as  we 
have  just  described  to  you. 


THE  A  B  C  OF  ELECTRICITY.  91 

BATTERIES. 

So  far  we  have  only  described  one  way  of  produc- 
ing electricity,  namely,  by  means  of  a  dynamo  ma- 
chine driven  by  steam  or  water  power.  The  supply 
of  electricity  so  obtained  is  regular  and  constant  as 
long  as  the  steam  or  water  power  is  applied  to  the 
dynamo. 

There  is  another  and  very  different  way  of  produc- 
ing electricity,  and  this  is  by  means  of  a  chemical 
process  in  what  is  called  a  battery. 

To  obtain  electricity  from  the  dynamo  we  must 
spend  money  for  the  coal  to  make  the  steam,  wThich 
operates  the  steam  engine,  or  for  the  water  which 
turns  the  water-wheel,  as  well  as  for  an  engineer  in 
both  cases.  When  we  obtain  electricity  from  a  bat- 
tery we  must  spend  money  for  the  chemicals  and 
metals  which  are  constantly  consumed  in  the  battery. 

PRIMARY    BATTERIES. 

An  electrical  battery  is  a  device  in  which  one  or 
more  chemical  substances  act  upon  a  metal  and  a 
carbon,  or  upon  two  different  metals,  producing 
thereby  a  current  of  electricity,  which  will  continue 
as  long  as  there  is  any  action  of  the  chemicals  upon 
the  metal  and  carbon,  or  upon  the  two  metals. 


92  THE  ABC  OF  ELECTRICITY. 

Batteries  for  producing  electricity  may  be  divided 
into  two  classes,  called  "  open  circuit "  "batteries  and 
"  closed  circuit "  batteries. 

Open  circuit  batteries  are  those  which  are  used 
where  the  electricity  is  not  required  constantly  with- 
out intermission,  for  instance,  in  telephones,  electric 
bells,  burglar  alarms,  gas  lighting,  annunciators,  etc. 

Closed  circuit  batteries  are  those  which  are  used 
where  the  effect  produced  must  be  continuous  every 
moment,  as,  for  instance,  in  electric  lights  and 
motors. 

The  open  circuit  battery  is  made  in  many  different 
ways,  so  we  only  describe  two  of  the  principal 
ones. 

As  we  told  you  in  an  early  part  of  this  book,  we 
do  not  know  just  what  electricity  is,  nor  why  it  is 
produced  under  the  conditions  existing  in  a  battery. 
But  we  do  know  that  by  following  certain  processes 
and  making  certain  chemical  combinations  we  can 
make  as  much  electricity  and  in  such  proportions  as 
we  want. 

The  two  metals,  or  the  metal  and  carbon,  in  a  bat- 
tery are  called  the  "  elements,"  and  to  these  are  con- 
nected the  wires  which  lead  from  the  battery  to  the 
instruments  to  be  worked  by  it. 

The  Leclanchg  Battery. — This  form  of  open  circuit 


THE  A  B  -C  OF  ELECTRICITY. 


93 


battery  consists  of  a  glass  jar  in  which  is  placed  the 

elements.     One  element  consists  of  a  rod  of  zinc, 

and  the  other  element  is  carbon  and  powdered  black 

oxide  of  manganese.    These  two  (the  carbon  and  black 

oxide  of  manganese)  are 

placed  in  an  earthenware 

vessel   called    a    "  porous 

cup."      This   is  simply  a 

small   jar    made    of    clay 

which  is  not  glazed.  Thus, 

the  liquid  which  is  in  the 

glass  jar  penetrates 
through  the  porous  cup 
to  the  carbon  and  man- 
ganese which  it  contains, 
and  so  the  chemicals  af- 
fect both  these  and  the 
zinc  at  once,  for,  in  order 
to  obtain  electricity,  you 
will  remember  that  the 
chemical  action  must  act 
at  the  same  time  upon 
both  the  elements  in  the  same  vessel. 

The  chemical  substance  used  in  this  battery  is  sal- 
ammoniac,  or  salts  of  ammonia.  A  certain  amount 
of  this  salt  is  placed  in  the  glass  jar  and  water  poured 
upon  it,  and  electricity  is  at  once  produced. 


Fig.  3i. 


94 


THE  A  B  C  OF  ELECTRICITY. 


The  "  Law '"  Battery. — The  elements  of  this  battery 
are  also  zinc  and  carbon,  which  are  contained  in 

a  glass  jar.  In 
this  battery,  how- 
ever, there  is  no 
porous  cup  used 
and  the  elements 
are  acted  upon 
directly  by  the 
liquid  (usually 
called  "  solution  ") 
I  in  the  jar. 

The  chemical 
substance  used  is 
the  same  as  in  the 
Leclanche  battery, 
namely,  sal-am- 
moniac, to  which 
water  is  added. 

The  Leclanch^  and  Law  batteries  are  used  mostly 
for  telephones,  electric  bells,  electric  gas  lighting, 
burglar  alarms,  hotel  annunciators,  etc. 

You  will  remember  that  in  telephones,  electric 
bells,  etc.,  the  electricity  is  not  doing  continuous  work, 
but  only  for  a  few  seconds  or  minutes  at  a  time,  con- 
sequently the  batteries  have  a  little  rest  in  between, 
if  only  for  a  few  seconds. 


Fig.  32, 


THE  A  B  C  OF  ELECTRICITY.  95 

Now,  if  we  were  to  attempt  to  use  open  circuit 
batteries  for  electric  lights  or  motors,  where  the  elec- 
tricity must  work  every  second,  the  batteries  would 
"  polarize,"  that  is  to  say,  they  would  only  work  a 
few  minutes  and  then  stop,  because  the  chemicals 
used  in  them  are  of  that  kind  that  they  will  only 
allow  the  battery  to  do  a  little  work  at  a  time. 

The  batteries  we  have  been  describing  will  do  the 
ordinary  work  for  which  they  are  intended  for  some- 
times a  year  without  requiring  any  attention,  but  if 
we  try  to  make  them  do  work  for  which  they  were 
not  intended,  they  would  only  last  a  few  days. 

If  we  should  want  to  operate  electric  lights  or 
motors  from  a  battery  we  must,  therefore,  use 

CLOSED  CIRCUIT  BATTERIES. 

There  are  a  very  large  numbers  of  ways  in  which 
closed  circuit  batteries  are  made,  but  as  the  main 
principles  are  very  much  alike,  we  will  only  describe 
two  general  kinds,  those  with  and  those  without  a 
porous  cup. 

In  the  first  place  we  must  state  that  closed  circuit 
batteries  usually  consist  of  a  glass  jar  and  two  ele- 
ments, carbon  and  zinc.  Sometimes  a  porous  cup  is 
used ;  for  what  reason  you  will  soon  learn. 

The  chemicals  that  are  used  are  usually  different 
from  those  used  in  the  open  circuit  batteries  and  are 
much  stronger.  These  chemicals  are  usually  sul- 


96  THE  A  B  C  OF  ELECTRICITY. 

phuric  acid  and  bi-chromate  of  potash  (or  chromic 
acid),  which  are  mixed  with  water. 

We  will  now  examine  two  of  the  types  of  closed 
circuit   batteries,   taking  first   the   one   without  the 
porous  cup,  of  which  the  Grenet  is  a  good  example. 
This  battery,  as   you  see,    con- 
sists of  a  glass  jar,  in   which  are 
placed  two  plates  of  carbon  and 
one  of  zinc.    The  latter  is  between 
the  two  carbon  plates  and  is  mov- 
able up  and  down,  so  that  it  may 
be  drawn   up  out  of  the  solution 
when  it  is  not  desired  to  use  the 
battery.     When  the  zinc  is  in  the 
solution  there  is  a  steady  and  con- 
tinuous current  of  electricity  de- 
veloped, which  can  be  taken  away 
by  wires  from  the  connections  on 
Fig.  33.  top  of  the  battery. 

If  the  zinc  were  left  in  the  solution  when  the 
battery  was  not  in  use,  the  acid  would  act  upon  it 
almost  as  much  as  though  the  electricity  were  not 
being  used,  and  thus  the  zinc  would  be  eaten  away 
and  the  acid  would  be  neutralized,  so  that  no  more 
action  could  be  had  when  we  wanted  more  elec- 
tricity. 

Now,  in  the  Grenet  battery  we  can  light  a  lamp  or 


THE  ABC  OF  ELECTRICITY.  97 

run  a  motor  for  several  hours  continuously,  but  at  the 
end  of  that  time  the  solution  would  become  black  and 
it  would  do  no  more  work.  Then  we  must  throw  out 
that  solution  and  put  in  fresh,  and  the  battery  will  do 
the  same  work  again,  and  so  on. 

If  you  should  only  want  to  light  your  lamp  or  run 
your  motor  for  a  few  minutes,  you  could  pull  the 
zinc  up  from  the  solution  and  put  it  down  again  when 
you  wanted  the  electricity  once  more.  The  carbon 
element  in  the  battery  is  not  consumed  by  the  acid, 
although  the  zinc  is- 

Now  you  will  see  the  use  of  the  porous  cup.  W« 
will  take  as  an  illustration  of  this  type  an  ordinary 
battery  in  which  a  porous  «up  is  used. 
.  Here,  you  will  see,  the 
carbon  is  placed  in  the 
porous  cup,  while  the 
zinc  is  outside  in  the 
glass  jar.  In  the  glass 
cell  with  the  zine  is  usu- 
ally used  water  made 
slightly  acid,  and  the 
strong  solution  of  sul- 
phuric acid  and  bi-chro 
mate  of  potash  (or  chro- 
mic acid)  is  poured  in 
the  porous  cup,  where  the  carbon  is  placed. 


Fig,  34. 


98  THE  A  13  C  OF  ELECTRICITY. 

The  strong  solution  penetrates  the  porous  cup  very 
slowly  and  gets  to  the  zinc,  when  it  immediately 
produces  a  current  of  electricity.  But,  the  acid 
does  not  get  at  the  zinc  so  freely  as  it  does  in  the 
battery  without  porous  cup,  and,  consequently, 
neither  the  acid  nor  zinc  are  so  rapidly  used  up. 

Where  porous  cups  are  used,  the  batteries  will  give 
a  continuous  current  for  a  very  much  longer  time 
than  without  them,  and  will,  sometimes,  give  many 
hours  work  every  day  for  several  months  without 
requiring  any  change  of  solution. 

Polarization. — There  is  one  other  reason  why  a 
longer  working  time  can  be  had  from  a  battery  with 
porous  cup,  and  that  is,  in  a  battery  without  porous 
cup,  the  action  of  the  acid  upon  the  zinc  is  so  rapid 
that  the  carbon  plates  become  covered  with  the  gas, 
and,  therefore,  the  proper  action  by  the  acid  cannot 
take  place  upon  them.  Thus,  the  battery  ceases  to 
work,  and  is  said  to  be  "polarized."  When  a  porous 
cup  is  used,  the  action  of  the  acid  upon  the  zinc  is 
slow  enough  to  give  off  only  a  small  amount  of  gas, 
and  thus  the  acid  has  a  chance  to  act  upon  the 
carbon  plates  and  develop  a  steady  current  of  elec- 
tricity. 

THE  WORK  DONE  BY  BATTERIES. 

The  pressure  and  quantity  of  electricity  given  off 


THE  ABC  OF  ELECTRICITY.  99 

continuously  by  open  and  closed  circuit  batteries  is 
very  different. 

The  pressure  (or  "  Electro-motive  force  ")  of  one 
cell  of  an  ordinary  open  circuit  battery  is  only  about 
one  volt,  and  the  current  is  usually  very  much  less 
than  one  ampere. 

In  a  closed  circuit  battery  described,  the  Electro- 
motive force  of  each  cell  is  about  two  volts,  while 
the  current  varies  from  1  to,  perhaps,  50  amperes, 
according  to  the  size  of  the  zinc  and  carbon  plates. 

It  would  not  matter  if  you  made  one  cell  as  big  as 
a  barrel,  nor  if  you  put  in  a  dozen  carbons  and  zincs, 
the  Electro-motive  force  would  not  exceed  two  volts  on 
steady  work,  but  the  ampere  capacity  would  be  greater 
in  number  than  in  a  smaller  cell  on  account  of  the 
larger  size  of  the  carbon  and  zinc  plates. 

Internal  Resistance. — There  is  one  other  point 
which  affects  the  number  of  amperes  which  can  be 
obtained  from  a  closed  circuit  battery,  and  that  is, 
whether  there  is  a  large  or  small  internal  resistance 
in  the  battery  itself. 

This  depends  upon  the  solution  which  is  used  and 
the  arrangement  of  the  plates. 

If  there  is  a  high  resistance  in  the  battery  itself 
(called  "  internal  resistance  "),  the  electricity  must 
do  work  to  overcome  this  resistance  before  it  can  get 


100  THE  A  B  C  OF  ELECTRICITY. 

out  of  the  battery  to  do  useful  work  through  the 
wires,  and,  consequently,  the  capacity  in  amperes  is 
limited. 

If,  on  the  other  hand,  there  is  very  little  resistance 
in  the  battery,  the  current  has  very  little  work  to 
flow  to  the  wires  leading  from  the  battery,  and  we 
can  get  a  larger  quantity,  or  greater  number  of  am- 
p£res. 

Thus,  you  will  see,  that  while  the  closed  circuit 
battery  is  the  strongest  and  will  do  all,  and  even 
more,  in  a  short  time,  than  the  open  circuit  battery, 
the  latter,  though  weaker,  will  do  about  as  much 
work  for  the  same  amount  of  zinc  and  carbon  as  the 
former,  but  takes  a  much  longer  time. 

BATTERIES   FOR   ELECTRIC   LIGHT. 

As  we  have  explained  to  you,  closed  circuit  bat- 
teries are  used  for  producing  incandescent  electric 
lights  in  small  numbers,  as  well  as  for  running 
motors. 

To  operate  incandescent  lights  a  number  of  batter- 
ies connected  together  are  used.  The  number  used 
depends  upon  the  pressure  which  the  lamps  require 
to  make  them  give  the  required  light.  We  will  now 
explain  how  the  batteries  are  connected  together  for 
this  purpose. 


THE  ABC  OF  ELECTRICITY. 


101 


Suppose  you  wished  to  light  an  incandescent  lamp 
of,  say,  three-candle  power,  which  required  six  volts. 
We  would  take  three  closed  circuit  batteries,  which 
would  each  give  two  volts,  and  connect  lay  a  piece  of 
wire  the  zinc  of  the  first  to  the  carbon  of  the  second, 
and  the  zinc  of  the  second  to  the  carbon  of  the  third, 
as  shown  in  the  sketch. 


c 

*-^ 

z 

c 

z 

c 

z 

^- 

Fig.  35. 

We  would  then  attach  a  wire  to  the  carbon  of  the 
first  and  one  to  the  zinc  of  the  third  and  there  would 
be  six  volts  pressure  in  these  two  wires,  which  would 
light  up  one  six-volt  lamp  nicely. 

This  is  called  connecting  in  series,  or  for  intensity. 

Now  if  each  of  these  cells  gave  ten  amperes  alone, 
the  three  will  only  give  ten  amperes  together  when 
they  are  connected  in  series. 

If  our  lamp  only  required  one  ampere  you  would 
naturally  think  that  ten  similar  lamps  put  on  the 
wires  would  give  as  good  light  as  the  one,  but  that 
is  not  so. 


103  TM-&  A  $  C  OF  ELECTRICITY. 

Although  you  raight  light  up  two  lamps,  the  press- 
ure would  drop  and  the  lights  would  become  less 
brilliant  if  you  put  on  the  whole  number.  So,  if  we 
wished  to  put  on  the  whole  ten  lights  we  would  con- 
nect another  battery  and  thus  increase  the  pressure, 
which  would  probably  make  these  ten  lamps  burn 
brightly. 

These  rules  hold  good  for  connecting  any  number 
of  batteries  for  lamps  of  any  number  of  volts,  that  is 
to  say,  there  should  be  calculated  about  two  volts  for 
each  cell  and  an  allowance  made  for  drop  in  pressure. 

CONNECTING  IN  MULTIPLE. 

There  is  another  way  of  connecting  batteries,  and 
that  is,  to  obtain  a  larger  number  of  amperes.  This 
is  called  connecting  in  Multiple  arc,  or  for  quantity. 

Let  us  take  again  for  an  illustration  the  three  cells 
giving  each  2  volts  and  10  amperes.  This  time  we 
connect  the  carbon  of  the  first  to  the  carbon  of  the 
second  and  the  carbon  of  the  second  to  that  of  the 
third ;  then  we  connect  the  zinc  of  the  first  to  that  of 
the  second,  and  the  zinc  of  the  second  to  that  of  the 
third,  as  shown  in  the  sketch. 


THE  ABC  OF  ELECTRICITY. 


103 


Fig.  36. 

We  then  attach  a  wire  to  the  zinc  and  one  to  the 
carbon  in  the  third  cell,  and  we  then  can  obtain  from 
these  two  wires  only  2  volts,  but  thirty  amperes. 

There  are  again  many  ways  of  connecting  several 
of  these  sets  together,  but  it  is  not  intended  in  this 
book  to  go  into  these  at  length,  for  the  reason  that 
we  only  set  out  to  give  a  simple  explanation  of  the 
first  principles  of  this  subject. 

We  shall  therefore  only  give  an  illustration  of  one 
more  method  of  connecting  batteries  which  will  be 
easy  to  understand.  This  is  called 

MULTIPLE    SERIES. 

The  sketch  we  have  last  given  shows  three  bat- 
teries connected  in  multiple.  These  we  will  call  set 
No.  1. 

Now,  suppose  we  take  three  more  batteries  exactly 
similar  and  connect  them  together  just  in  the  same 
manner.  Let  us  call  this  set  No.  2.  Now  take  the 


104  THE  A  V  C  OF  ELECTRICITY. 

wire  leading  from  the  carbon  of  set  No.  2  and  con- 
nect it  with  the  wire  leading  from  the  zinc  of  set 
No.  1.  Then  take  a  wire  leading  from  the  zinc  of  set 
No.  2  and  a  wire  leading  from  the  carbon  of  set  No.  1, 
and  connect  them  with  the  lamps  or  motors.  These 
two  sets,  being  connected  in  multiple  series,  we  shall 
get  4  volts  and  30  amperes. 

This  is  called  connecting  in  multiples  series,  and 
may  be  extended  indefinitely  with  any  number  of 
batteries. 

We  should  add  that  one  of  the  elements  in  a  bat- 
tery is  called  u  positive  "  and  the  other  "negative." 

SECONDARY,  OK  STORAGE  BATTERIES. 

The  open  and  closed  circuit  batteries  we  have  so 
far  described  are  used  to  produce  electricity  by  the 
action  of  the  chemicals  upon  the  elements  contained 
in  them.  They  are  called  Primary  Batteries. 

The  batteries  which  we  will  now  tell  you  of  are 
called  Secondary,  or  Storage,  Batteries,  and  do  not  of 
themselves  make  any  primary  current,  but  simply  act 
as  reservoirs  to  hold  the  energy  of  the  electric  current 
which  is  led  into  them  from  a  dynamo  or  primary  bat- 
tery. At  the  proper  time  and  under  proper  conditions 
these  secondary  batteries  will  give  back  the  energy  of 
the  electric  current  which  has  been  stored  in  them. 


THE  A  n  C  OF  ELECTRICITY.  105 

A  secondary  Lattery  usually  consists  of  a  glass  jar 
containing  lead  plates  and  some  water  made  slightly 
acid. 

There  are  always  at  least  two  lead  plates  in  a  sec- 
ondary battery,  although  there  may  be  any  number 
above  that.  For  the  sake  of  making  a  more  clear 
explanation  to  you,  we  will  take  as  an  illustration  a 
battery  with  only  two  plates. 

We  have  then  a  glass  jar  containing  two  lead  plates 
and  some  acidulated  water.  These  plates  are  called 
the  "  electrodes,"  and  one  is  the  positive  and  the 
other  the  negative  electrode. 

The  positive  electrode  is  a  sheet  of  lead  upon 
which  is  spread  a  paste  made  of  red  lead.  The  neg- 
ative electrode  is  a  similar  sheet  of  lead  upon  which 
is  spread  a  paste  made  of  litharge. 

Now,  when  these  plates  are  thus-  prepared  they  are 
put  into  the  acidulated  water  in  the  glass  jar  and  a 
wire  from  each  plate  is  connected  with  the  wires 
from  a  dynamo  or  a  primary  battery,  just  as  a  lamp 
would  be  connected. 

The  electricity  then  goes  into  the  secondary  bat- 
tery, entering  by  one  plate  and  coming  out  by  the 
other.  These  plates  and  the  paste  upon  them  offer 
some  resistance  or  opposition  to  the  passage  of  the 
current,  so  the  electricity  must  do  some  work  to  get 


106  THE  A  B  C  OF  ELECTRICITY. 

from  one  to  the  other.  The  work  it  does  in  this  case 
is  to  so  act  upon  the  paste  that  its  chemical  nature  is 
changed. 

So,  after  the  primary  current  has  been  passed  from 
one  plate  to  the  other  for  some  time,  the  secondary 
battery  is  disconnected,  being  now  "  charged." 

The  paste  on  the  lead  plates  is  now  changed,  the 
paste  on  the  positive  electrode  having  been  trans- 
formed into  peroxide  of  lead,  and  that  on  the  neg- 
ative electrode  into  spongy  lead. 

The  plates  being  still  in  acidulated  water,  the  paste 
upon  them  begins  to  work  to  get  back  to  its  original 
nature,  and  if  it  is  left  to  itself  long  enough  will 
gradually  get  back  to  it. 

Now,  this  working  of  the  plate  causes  a  current  of 
electricity  in  the  battery,  which  we  can  use  to  light 
lamps  or  to  do  other  useful  work  1  y  attaching  wires 
to  the  lead  plates  and  using  the  current  just  as  we 
would  if  it  came  from  a  dynamo  or  primary  battery. 

When  the  paste  has  returned  to  about  its  first  con- 
dition the  secondary  battery  is  discharged,  and  may 
then  be  again  charged  and  discharged  a  great  many 
times  in  just  the  same  way. 

CONNECTING  SECONDARY  BATTERIES. 

One  cell  of  a  secondary  battery  will  give  about  two 
volts,  no  matter  what  its  size  or  the  number  of  plates 


THE  A  B  C  OF  ELECTRICITY.  107 

may  be.  When  there  are  more  than  two  plates  in 
one  cell,  all  the  positives  are  connected  together  by  a 
strip  of  lead,  and  all  the  negatives  are  connected 
together  in  the  same  way. 

Although  we  cannot  obtain  more  than  two  volts 
electro-motive  force  from  one  cell,  we  can  obtain  a 
greater  ampere  capacity  by  using  large  plates  instead 
of  small  ones,  or  by  using  a  larger  number  of  small 
size. 

The  same  effects  are  produced  by  connecting  the 
cells  in  series,  or  multiple,  or  multiple-series,  as  we 
showed  you  in  regard  to  primary  batteries ;  and  the 
secondary  batteries  may  be  charged  as  well  as  dis- 
charged when  connected  in  any  one  of  these  ways. 

CHARGING  CURRENT. 

The  current  which  is  used  for  charging  must  always 
be  greater*  in  pressure  than  that  of  the  secondary  bat- 
teries which  are  being  charged.  If  it  is  not,  the  sec- 
ondary batteries  will  be  the  stronger  of  the  two  and 
will  overpower  the  charging  current  and  so  discharge 
themselves. 


108  THE  A  B  C  OF  ELECTRICITY. 


CONCLUSION. 

We  will  now  bring  this  little  volume  to  a  close, 
having  given  you  a  brief  outline  of  the  simplest  rudi- 
ments of  that  wonderful  power  of  nature.  Electricity. 

We  may  compare  this  subject  to  a  beautiful  house, 
the  inside  of  which  you  would  like  to  examine  from 
top  to  bottom.  We  have  opened  the  door  for  you, 
now  walk  in  and  examine  everything.  There  may 
be  a  great  many  stairs  to  climb,  but  what  you  see  and 
learn  will  repay  for  all  the  trouble. 


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